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CBSE Class 10 Science 2026 — Paper 31/4/3

80 marks · 3 hours · 39 questions (45 with the OR choices)

32 of its 45 questions also appear in 31/4/1 or 31/4/2; 13 are only in this paper.

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Questions 1–9 · 1 mark each

  1. Q1 1 mark

    Also in 31/4/1 (Q3), 31/4/2 (Q2)

    Given below are some of the statements regarding our environment :
    1. (i)Change in our life-styles have resulted in greater amounts of waste material generation.
    2. (ii)Changes in attitude have resulted in use of more disposable things.
    3. (iii)Changes in packaging has resulted in much of our waste becoming non-biodegradable.
    4. (iv)Organic farming. Which amongst these is not leading to any damage of environment ?
    1. (a)(i), (ii), (iii)
    2. (b)(iv)
    3. (c)(i) and (iii)
    4. (d)(ii) and (iv)
    Show answer
    (b) (iv)
    Step-by-step solution →
  2. Q2 1 mark

    Also in 31/4/1 (Q1)

    Observe the given figure and select the statement that correctly states how these fungi obtain nutrition.
    Bread mould Fungi body Bread
    1. (a)By eating the bread on which it is growing.
    2. (b)By using nutrients from the bread to prepare their own food.
    3. (c)By breaking down the nutrients of bread outside the body and then absorbing them.
    4. (d)By allowing other organisms to grow on the bread and then consuming them.
    Show answer
    (c) By breaking down the nutrients of bread outside the body and then absorbing them.
    Step-by-step solution →
  3. Q3 1 mark

    Also in 31/4/1 (Q2), 31/4/2 (Q1)

    If the part 'P' of the flower is removed, which of the following processes will not take place ?
    P
    1. (a)Formation of pollens
    2. (b)Formation of flower
    3. (c)Formation of fruit
    4. (d)Formation of seed
    Show answer
    (c) Formation of fruit
    Step-by-step solution →
  4. Q4 1 mark
    Four chambered heart is a characteristic of :
    1. (a)Fishes
    2. (b)Amphibians
    3. (c)Reptiles
    4. (d)Mammals
    Show answer
    (d) Mammals
    Step-by-step solution →
  5. Q5 1 mark
    Translocation is the process in which plants deliver :
    1. (a)Minerals from leaves to other parts of the plant.
    2. (b)Plant growth hormones from leaves to other parts of the plant.
    3. (c)Water and inorganic substances from leaves to other parts of the plant.
    4. (d)Organic substances from leaves to the other parts of the plant.
    Show answer
    (d) Organic substances from leaves to the other parts of the plant.
    Step-by-step solution →
  6. Q6 1 mark

    Also in 31/4/1 (Q7), 31/4/2 (Q5)

    In human beings the oxygen rich blood is pumped out to the body by :
    1. (a)contraction of right atrium
    2. (b)relaxation of left ventricle
    3. (c)contraction of right ventricle
    4. (d)contraction of left ventricle
    Show answer
    (d) contraction of left ventricle
    Step-by-step solution →
  7. Q7 1 mark

    Also in 31/4/1 (Q6), 31/4/2 (Q4)

    Two pea plants, one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds were crossed with each other which produced progeny that have only round yellow (RrYy) seeds. When plants are self-pollinated, the progeny will have which new combination of characters, as compared to the parents :
    1. (i)Round, yellow
    2. (ii)Round, green
    3. (iii)Wrinkled, yellow
    4. (iv)Wrinkled, green Correct options are :
    1. (a)(i) and (ii)
    2. (b)(i) and (iv)
    3. (c)(ii) and (iv)
    4. (d)(i) and (iii)
    Show answer
    (b) (i) and (iv)
    Step-by-step solution →
  8. Q8 1 mark

    Also in 31/4/1 (Q9), 31/4/2 (Q8)

    This question consists of two statements — Assertion (A) and Reason (R). Answer the question by selecting the appropriate option from (a), (b), (c) and (d) given below :

    Assertion (A): Highest percentage of pesticides is found in tertiary consumers in a food chain.

    Reason (R): Chemicals / pesticides get accumulated progressively at each trophic level.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    Step-by-step solution →
  9. Q9 1 mark

    Also in 31/4/1 (Q8)

    This question consists of two statements — Assertion (A) and Reason (R). Answer the question by selecting the appropriate option from (a), (b), (c) and (d) given below :

    Assertion (A): Variations are not often seen in off-springs produced by asexual reproduction.

    Reason (R): DNA molecule generated by replication is not similar to the original DNA.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (c) Assertion (A) is true, but Reason (R) is false.
    Step-by-step solution →

Questions 10–12 · 2 marks each

  1. Q10 2 marks
    What are decomposers ? List two important roles they play in the environment.
    Show answer

    Decomposers are bacteria and fungi that break dead remains into simple substances; they replenish the soil and air and keep the environment clean.

    Decomposers are micro-organisms, mainly bacteria and fungi, that feed on the dead remains and waste products of plants and animals and break their complex organic compounds down into simple inorganic substances such as carbon dioxide, water, nitrates and minerals. Two important roles they play in the environment are: (i) They replenish the soil and the air. The nutrients locked inside dead bodies are released back into the soil and the atmosphere, where green plants absorb them and use them again, so the same stock of nutrients circulates indefinitely and the nitrogen, carbon and other biogeochemical cycles keep turning. (ii) They keep the environment clean. They dispose of the dead bodies, fallen leaves, dung and other organic wastes that would otherwise pile up on the surface of the earth, take up space and spread disease, which is also why they are put to work in compost pits and sewage treatment plants.
    Step-by-step solution →
  2. Q11 2 marks
    The leaves of a plant first prepares food 'P' by photo-synthesis. Food 'P' is then converted to food 'Q', which is stored in the leaves if not used immediately. What are 'P' and 'Q' ? What are the raw materials and conditions required for synthesis of 'P' ?
    Show answer

    P is glucose and Q is starch; photosynthesis needs carbon dioxide and water as raw materials, and sunlight and chlorophyll as conditions.

    'P' is glucose, a simple carbohydrate of formula . It is the first food the leaf prepares by photosynthesis. 'Q' is starch. The glucose the plant does not use immediately is converted into starch, which is insoluble and is stored in the leaves as the plant's internal energy reserve, to be broken back down to glucose when it is needed. The raw materials required for the synthesis of 'P' are carbon dioxide, taken from the air through the stomata of the leaf, and water, absorbed from the soil by the roots and carried up in the xylem. The conditions required are sunlight, which supplies the energy, and chlorophyll, the green pigment in the chloroplasts that absorbs the light energy and converts it into chemical energy. In symbols: .
    Step-by-step solution →
  3. Q12(a) 2 marks

    Also in 31/4/1 (Q12(a)), 31/4/2 (Q10(a))

    Varun is diabetic. His latest ultrasound reports showed a blockage in his pancreatic duct. How will this affect the dual functioning of the pancreas?
    Show answer

    The blocked duct affects digestion, as pancreatic juice cannot reach the small intestine, but insulin reaches the blood without the duct.

    The pancreas is a dual gland. Exocrine function: it secretes pancreatic juice, containing trypsin, pancreatic amylase and lipase, which reaches the small intestine (duodenum) through the pancreatic duct. With the duct blocked, these digestive enzymes cannot be transported to the small intestine, so the digestion of proteins, carbohydrates and fats will be affected. Endocrine function: its islets of Langerhans secrete insulin directly into the blood, without using the duct. Varun is diabetic, so his insulin secretion is already affected; the blockage does not change it further, because insulin does not travel through the duct.
    Step-by-step solution →
    OR
    Q12(b) 2 marks

    Also in 31/4/1 (Q12(b)), 31/4/2 (Q10(b))

    Sunil unconsciously touched the hot iron rod and immediately withdrew his hand. Which type of action is involved? Also define this action. Draw a flow chart to show the path followed for this action.
    Show answer

    The action is a reflex action: a rapid, automatic, involuntary response to a stimulus, without conscious thinking.

    The action involved is a **reflex action**. A reflex action is a sudden, rapid, automatic and involuntary response of the body to a stimulus, which occurs without conscious thinking; the withdrawal of the hand is controlled by the spinal cord. The path followed is the reflex arc: Stimulus (heat of the hot iron rod) Receptor (heat and pain receptors in the skin of the hand) Sensory neuron Spinal cord (relay neuron) Motor neuron Effector (muscle of the arm) Response (the hand is withdrawn).
    Step-by-step solution →

Questions 13–14 · 3 marks each

  1. Q13 3 marks
    Use the following information for Pea plants : Dominant allele for tall plants – T Recessive allele for short plants – t Dominant allele for purple flowers – P Recessive allele for white flowers – p
    1. (a)Perform a cross between pure plant dominant for both the traits with another plant which is recessive for both the traits and work out the progeny upto generation.
    2. (b)What is the probability of obtaining tall plants with white flowers in progeny ?
    Show answer

    shows , and the probability of a tall plant with white flowers is .

    (a) The pure dominant parent is (tall, purple) and the parent recessive for both traits is (short, white). Their only gametes are and , so the whole is - every plant tall with purple flowers. Self-pollinating the gives ; each parent now forms four kinds of gamete, , , and , and the sixteen boxes of the Punnett square give an of tall purple tall white short purple short white (genotypes ). (b) Tall plants with white flowers occupy of the boxes, so the probability is , that is or . Their genotypes are and .
    Step-by-step solution →
  2. Q14 3 marks

    Also in 31/4/1 (Q13)

    Give reasons for the following:
    1. (a)Adrenal gland is known as the stress gland of the body.
    2. (b)Prenatal sex determination is banned in India.
    3. (c)Vegetative propagation is advantageous in some plants.
    Show answer

    Adrenaline readies the body for stress; the ban stops female foeticide; vegetative propagation keeps the parent's characters and gives earlier flowering.

    (a) The adrenal glands, one above each kidney, secrete adrenaline straight into the blood whenever the body meets fear, anger or any other stressful situation. Adrenaline makes the heart beat faster so that more oxygen reaches the muscles, raises the breathing rate, and diverts blood from the skin and the digestive system to the skeletal muscles, thus preparing the body to fight or to run. Because it is the gland that readies the body to meet stress, it is called the stress or emergency gland. (b) The techniques were being misused for female foeticide, the selective abortion of female foetuses, which made the child sex ratio fall sharply and threatened the balance of the population. Prenatal sex determination is therefore prohibited by law in India, to stop female foeticide and to protect the girl child. (c) Because only a part of one parent plant is used and no gametes are involved, the new plants are genetically identical to the parent and keep all its desirable characters; plants that have lost the capacity to produce seeds, such as banana, orange, rose and jasmine, can be multiplied only in this way; and since the new plant begins from an already mature part, it bears flowers and fruit earlier than a plant grown from seed.
    Step-by-step solution →

Question 15 · 4 marks

  1. Q15 4 marks

    Also in 31/4/1 (Q15), 31/4/2 (Q15)

    Plants exhibit movements in response to various environmental stimuli to adopt and survive in their surroundings. These movements, influenced by external factors such as light, gravity, water and chemicals are regulated by specific plant hormones. For example, the differential growth of plant parts allows them to bend, grow or orient themselves in particular directions. Roots and shoots often show contrasting response to the same stimulus, highlighting the complex mechanisms involved in plant growth and development.
    1. (a)Why is hydrotropism essential for plants ?
    2. (b)What role does auxin play in the growth of plants ?
    3. (c)Differentiate between movement shown by the sensitive plant and tropic movement by plants (Two points).
    4. (c)OR : How does movement of roots differ from that of shoots in response to gravity and light ?
    Show answer

    Roots grow towards water; auxin lengthens cells so shoots bend to light; sensitive plants move without growth; roots and shoots respond oppositely.

    (a) A plant is fixed in one place and cannot move to find water, so its roots must grow to reach it. Roots are positively hydrotropic: they bend and grow towards the area of water availability in the soil, so that they can absorb water and the minerals dissolved in it, even when the water does not lie directly below the seed. That water is needed for photosynthesis, for carrying minerals up the plant, for keeping cells turgid and for transpiration, and the spreading root system it produces also anchors the plant. (b) Auxin is a hormone made at the tip of the shoot. It makes cells grow longer, so it controls the rate and the direction of growth. When light comes from one side, auxin diffuses to the shaded side; those cells elongate more than the ones in the light, so that side becomes longer and the shoot bends towards the light. (c) Two differences. First, the sensitive plant's movement is non-directional - the leaflets fold the same way whichever side is touched - whereas a tropic movement is directional, its direction set by the direction of the stimulus. Second, the sensitive plant's movement involves no growth: cells at the base of the leaflets rapidly lose water, so it takes seconds and is reversible, whereas a tropic movement is a slow, permanent growth movement caused by unequal cell elongation. OR (c) Roots and shoots respond in opposite directions. To gravity, roots grow downwards in the direction of gravity (positive geotropism) while shoots grow upwards against it (negative geotropism). To light, shoots grow towards the light (positive phototropism) while roots grow away from it (negative phototropism).
    Step-by-step solution →

Question 16 · 5 marks

  1. Q16(a) 5 marks

    Also in 31/4/1 (Q16(a)), 31/4/2 (Q16(a))

    1. (a)Draw a labelled diagram showing open and closed stomatal pore.
    2. (b)List the main events that occur during the process of photo-synthesis.
    3. (c)Write a balanced chemical equation showing photo-synthesis in plants.
    Show answer

    Turgid guard cells open the pore and flaccid ones close it; photosynthesis absorbs light, splits water and reduces carbon dioxide to carbohydrate.

    (a) Two guard cells face each other around the pore. In the open stoma they are turgid and bow apart, leaving a wide pore between them; in the closed stoma they are flaccid and their inner walls press together, so the pore is shut. Label the guard cells, the chloroplasts in them and the stomatal pore. (b) The main events are: (i) Absorption of light energy by chlorophyll; (ii) Conversion of light energy into chemical energy and splitting of water molecules into hydrogen and oxygen; (iii) Reduction of carbon dioxide to carbohydrates. These events need not follow one another immediately. (c) , where is glucose. Cancelling the six molecules of water that appear on both sides gives the equivalent net equation , which is also balanced.
    Step-by-step solution →
    OR
    Q16(b) 5 marks

    Also in 31/4/1 (Q16(b)), 31/4/2 (Q16(b))

    1. (a)Draw a well-labelled diagram of nephron and label atleast 4 of its parts.
    2. (b)Write the role of capillary cluster inside Bowman's capsule.
    3. (c)What is meant by selective reabsorption ?
    Show answer

    The glomerulus filters blood under high pressure into Bowman's capsule; the tubule then selectively reabsorbs useful substances, leaving wastes to form urine.

    (a) The nephron runs from Bowman's capsule, which cups the glomerulus, into the proximal convoluted tubule, then down and up the loop of Henle, into the distal convoluted tubule and finally into the collecting duct; blood enters the glomerulus by the afferent arteriole and leaves by the narrower efferent arteriole. Any four of these parts satisfy the question, and the diagram labels eight. (b) The capillary cluster is the glomerulus. Because the afferent arteriole bringing blood in is wider than the efferent arteriole taking it away, the blood pressure inside the tuft is high, and under that pressure the glomerulus filters the blood: water, glucose, amino acids, salts, urea and other small molecules are forced through the thin capillary walls into Bowman's capsule, while blood cells and large plasma proteins are too big to pass and remain in the blood. The fluid collected is the glomerular filtrate, and the process is ultrafiltration. (c) Selective reabsorption is the taking back into the blood, from the filtrate flowing along the tubule, of the substances the body still needs, while the wastes are left behind. Glucose, amino acids, most salts and a major part of the water are reabsorbed, chiefly in the proximal convoluted tubule, whereas the wastes such as urea, together with the excess salts and the remaining water, pass on to form urine. It is selective because the useful substances are recovered in preference to the wastes, and the amount of water taken back depends on how much excess water the body has and how much dissolved waste it must excrete.
    Step-by-step solution →

Questions 17–24 · 1 mark each

  1. Q17 1 mark

    Also in 31/4/1 (Q19), 31/4/2 (Q20)

    An aqueous solution turns red litmus blue. Excess addition of which of the following solution would reverse the change ?
    1. (a)Sodium hydroxide
    2. (b)Hydrochloric acid
    3. (c)Baking soda
    4. (d)Slaked lime
    Show answer
    (b) Hydrochloric acid
    Step-by-step solution →
  2. Q18 1 mark

    Also in 31/4/1 (Q20), 31/4/2 (Q18)

    While washing dirty clothes by soap, micelles are formed. Select the correct statement about micelles.
    1. (a)The hydrophobic tail of the soap molecule is in the interior of the cluster, whereas hydrophilic end is on the surface of the cluster.
    2. (b)The hydrophobic tail is on the surface of the cluster, whereas hydrophilic end is in the interior of cluster.
    3. (c)Both hydrophobic tail and hydrophilic end are in the interior of the cluster.
    4. (d)Both hydrophobic tail and hydrophilic end are on the surface of the cluster.
    Show answer
    (a) The hydrophobic tail of the soap molecule is in the interior of the cluster, whereas hydrophilic end is on the surface of the cluster.
    Step-by-step solution →
  3. Q19 1 mark

    Also in 31/4/1 (Q21)

    Which one of the following metals does not react with cold water ?
    1. (a)Sodium
    2. (b)Potassium
    3. (c)Calcium
    4. (d)Magnesium
    Show answer
    (d) Magnesium
    Step-by-step solution →
  4. Q20 1 mark

    Also in 31/4/1 (Q18), 31/4/2 (Q19)

    The above reaction is an example of -
    1. (a)Displacement Reaction
    2. (b)Endothermic Reaction
    3. (c)Exothermic Reaction
    4. (d)Neutralisation Reaction
    Show answer
    (c) Exothermic Reaction
    Step-by-step solution →
  5. Q21 1 mark

    Also in 31/4/1 (Q17)

    The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is
    1. (a)
    2. (b)
    3. (c)
    4. (d)
    Show answer
    (b)
    Step-by-step solution →
  6. Q22 1 mark
    Solder is an alloy of
    1. (a)copper and zinc
    2. (b)lead and zinc
    3. (c)lead and tin
    4. (d)copper and tin
    Show answer
    (c) lead and tin
    Step-by-step solution →
  7. Q23 1 mark
    Which one of the following chemicals is used in soda-acid fire-extinguishers ?
    1. (a)Sodium carbonate
    2. (b)Sodium hydrogen carbonate
    3. (c)Sodium hydroxide
    4. (d)Sodium acetate
    Show answer
    (b) Sodium hydrogen carbonate
    Step-by-step solution →
  8. Q24 1 mark

    Also in 31/4/1 (Q24), 31/4/2 (Q24)

    In the question, two statements are given – One labelled as Assertion (A) and other labelled as Reason (R). Write the correct answer selecting the appropriate option from (a), (b), (c) & (d) given below :

    Assertion (A): Pure ethanoic acid is also known as glacial acetic acid.

    Reason (R): Pure ethanoic acid often freezes during winter due to its low melting point of 290 K.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    Step-by-step solution →

Question 25 · 2 marks

  1. Q25 2 marks
    Write the balanced chemical equation for the preparation of :
    1. (a)Sodium hydroxide by electrolysis of brine solution
    2. (b)Sodium carbonate
    Show answer

    Electrolysis of brine gives , and ; heating gives .

    (a) Sodium hydroxide is prepared by the chlor-alkali process, the electrolysis of concentrated brine: . Chlorine is liberated at the anode, hydrogen at the cathode, and the sodium hydroxide is left in the solution near the cathode. (b) Sodium carbonate is prepared by heating sodium hydrogen carbonate, which the Solvay (ammonia-soda) process itself makes from brine: , the hydrogen carbonate coming from .
    Step-by-step solution →

Questions 26–27 · 3 marks each

  1. Q26(a) 3 marks

    Also in 31/4/1 (Q27(a)), 31/4/2 (Q27(a))

    (i) Which method will be used to convert each of them to their respective metal oxides ?
    1. (a)Carbonate ore
    2. (b)Sulphide ore (ii) Write a chemical reaction to illustrate the use of aluminium for joining cracked railway tracks. (iii) During extraction of metals, electrolytic refining is used to obtain pure metals. Which material will be used as anode and cathode for the refining of copper metal by this process ?
    Show answer

    Carbonate ore: calcination; sulphide ore: roasting; the thermite reaction welds rails; impure copper is the anode and pure copper the cathode.

    (i) (a) A carbonate ore is converted to its oxide by calcination, that is by heating it strongly in a limited supply of air: . (b) A sulphide ore is converted to its oxide by roasting, that is by heating it strongly in excess air: . (ii) The thermite reaction is used: . It is so strongly exothermic that the iron is produced molten, and it runs into the crack between the rails and solidifies there, welding them. (iii) Anode: a thick block of impure copper. Cathode: a thin strip or sheet of pure copper. The electrolyte is copper sulphate solution acidified with sulphuric acid, and the insoluble impurities collect below the anode as anode mud.
    Step-by-step solution →
    OR
    Q26(b) 3 marks

    Also in 31/4/1 (Q27(b)), 31/4/2 (Q27(b))

    1. (i)Write all the reactions involved in the extraction of from .
    2. (ii)Hydrogen gas is not evolved when most of the metals react with nitric acid. Give reason.
    Show answer

    Zinc sulphide is roasted to zinc oxide, then reduced with carbon; nitric acid oxidises the hydrogen formed to water.

    (i) Zinc is extracted from zinc blende in two reactions. Roasting, in which the concentrated ore is heated in excess air: . Reduction, in which the oxide is heated with coke: . The zinc obtained is finally purified by electrolytic refining. (ii) Nitric acid is a strong oxidising agent. The hydrogen that the metal displaces from it is oxidised to water as soon as it is formed, while the nitric acid is itself reduced to an oxide of nitrogen (, or according to the concentration of the acid and the metal used). No hydrogen therefore escapes as gas. Magnesium and manganese with very dilute nitric acid are the exceptions and do evolve hydrogen.
    Step-by-step solution →
  2. Q27 3 marks
    Answer the following :
    1. (a)Write two observations when green coloured crystals of ferrous sulphate are heated in a boiling tube.
    2. (b)Why brown coloured copper powder turns black on heating ?
    3. (c)What happens when limestone is heated strongly ?
    Show answer

    Ferrous sulphate turns white, then reddish-brown, giving and ; copper forms black copper(II) oxide; limestone gives quicklime and carbon dioxide.

    (a) Two observations. First, the green colour of the crystals is lost: on heating, the crystals of give up their water of crystallisation and turn white, and on stronger heating the residue left in the tube turns reddish-brown, since it is ferric oxide, . Second, gases with the characteristic choking smell of burning sulphur - sulphur dioxide and sulphur trioxide - are given off from the mouth of the boiling tube. The reaction is a thermal decomposition: , followed by . (b) Because the hot copper combines with the oxygen of the air and its surface is converted into copper(II) oxide, which is black. Copper is oxidised, and the change is a combination reaction: , brown copper to black copper(II) oxide. (c) Limestone, which is calcium carbonate, decomposes. It leaves a white residue of calcium oxide, called quicklime, and gives off carbon dioxide gas, which turns lime water milky. This thermal decomposition of a carbonate is called calcination: .
    Step-by-step solution →

Question 28 · 4 marks

  1. Q28 4 marks

    Also in 31/4/1 (Q28), 31/4/2 (Q28)

    The pH plays an important role in our daily life. Strength of acids and bases depends on the number of ions and ions produced by these respectively. pH scale helps in predicting the strength of acids and bases by measuring hydrogen ion concentration in a solution. Answer the following :
    1. (a)What type of indicator is used to predict how strong an acid or base is ?[1]
    2. (b)Three solutions A, B and C showed pH as 3, 5 and 7. Which solution has the highest concentration of ions ?[1]
    3. (c)What are strong acids and weak acids ?[2]
    4. (c)OR : (i) Under what condition is rainwater called acid rain ? (ii) In the following acids, identify weak acids : Nitric acid, hydrochloric acid, acetic acid, sulphuric acid, formic acid.[2]
    Show answer

    A universal indicator shows strength; solution A (pH 3) has the highest ; strong acids ionise completely, weak acids partially.

    (a) A universal indicator - a mixture of several indicators, used as a solution or as pH paper. It gives a different colour at each pH, so its colour reports how strong the acid or base is, which litmus or phenolphthalein cannot do. (b) Solution A. Since , the concentrations are mol/L in A, mol/L in B and mol/L in C, so the smallest pH, 3, carries the highest hydrogen ion concentration. (c) A strong acid ionises completely in water and so gives a large number of ions (for example , , ); a weak acid ionises only partially and so gives far fewer ions (for example , ). OR (c) (i) Rain water is called acid rain when its pH is less than 5.6. (ii) The weak acids in the list are acetic acid and formic acid; nitric, hydrochloric and sulphuric acids are strong.
    Step-by-step solution →

Question 29 · 5 marks

  1. Q29(a) 5 marks

    Also in 31/4/1 (Q29(a)), 31/4/2 (Q29(a))

    1. (i)Carbon cannot form cation and anion. Explain.
    2. (ii)Define homologous series of carbon compounds. Why are the melting and boiling points of higher than or ?
    3. (iii)What happens when ethanol is heated with acidified potassium dichromate ?
    Show answer

    Carbon cannot lose or gain four electrons, so it shares them; heavier has stronger intermolecular forces; acidified dichromate oxidises ethanol to ethanoic acid.

    (i) Carbon has four valence electrons (configuration ). To form it would have to lose all four, which needs an enormous amount of energy and would leave a nucleus of six protons holding only two electrons; to form it would have to gain four, and a nucleus of only six protons cannot hold on to ten electrons. Carbon therefore shares its four valence electrons instead, forming four covalent bonds - it is tetravalent. (ii) A homologous series is a series of carbon compounds having the same general formula and the same functional group, in which successive members differ by one unit, that is by 14 u; the members have similar chemical properties and a gradual gradation in physical properties. (58 u) is a larger, heavier molecule than (44 u) or (30 u), so the intermolecular forces of attraction between its molecules are stronger and more energy is needed to separate them; hence its higher melting and boiling points. (iii) Acidified potassium dichromate acts as an oxidising agent and oxidises ethanol to ethanoic acid, the orange colour of the dichromate turning green:
    Step-by-step solution →
    OR
    Q29(b) 5 marks

    Also in 31/4/1 (Q29(b)), 31/4/2 (Q29(b))

    1. (i)How would you name the following : I. II.
    2. (ii)When ethanol reacts with ethanoic acid in the presence of conc. , a substance with sweet smell is produced. Answer the following : I. State the class of compounds to which the sweet smelling compounds belong. II. Write the chemical equation for the reaction.
    3. (iii)Why soaps do not produce foam with hard water ?
    I. CH₃ – CH₂ – C = O H II. CH₃ – C ≡ CH
    Show answer

    Propanal and propyne; the sweet-smelling compounds are esters; soap forms insoluble scum with the calcium and magnesium ions of hard water, so no foam.

    (i) I. Propanal (), an aldehyde. II. Propyne (), also written prop-1-yne. (ii) I. The sweet smelling compounds are esters, and the reaction that forms them is called esterification. II. , that is ethanoic acid and ethanol give ethyl ethanoate and water. (iii) Hard water contains and ions. These react with soap, which is the sodium salt of a long chain carboxylic acid, to form insoluble calcium and magnesium salts of that acid - a curdy white precipitate called scum. The soap is used up as scum instead of dissolving to form micelles, so it does not lather and a large amount of soap is wasted.
    Step-by-step solution →

Questions 30–32 · 1 mark each

  1. Q30 1 mark

    Also in 31/4/1 (Q30), 31/4/2 (Q31)

    The pair of eye parts responsible for admitting different amount of light in to the eyes is
    1. (a)Iris and pupil
    2. (b)Ciliary muscles and pupil
    3. (c)Retina and Iris
    4. (d)Ciliary muscles and cornea
    Show answer
    (a) Iris and pupil
    Step-by-step solution →
  2. Q31 1 mark

    Also in 31/4/1 (Q31), 31/4/2 (Q30)

    The vision defect which arises due to gradual weakening of the ciliary muscles and diminishing flexibility of eye lens is :
    1. (a)Myopia
    2. (b)Hypermetropia
    3. (c)Presbyopia
    4. (d)Myopia and hypermetropia both
    Show answer
    (c) Presbyopia
    Step-by-step solution →
  3. Q32 1 mark

    Also in 31/4/1 (Q32), 31/4/2 (Q32)

    For this question, two statements are given – one labelled as Assertion (A) and other labelled as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) & (d) as given below :

    Assertion (A): With the help of compass, magnetic field lines can be traced outside the bar magnet.

    Reason (R): The north pole of a compass needle always points towards the south pole of the magnet when brought close to it.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
    3. (c)Assertion (A) is true, but Reason (R) is false.
    4. (d)Assertion (A) is false, but Reason (R) is true.
    Show answer
    (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
    Step-by-step solution →

Questions 33–34 · 2 marks each

  1. Q33(a) 2 marks

    Also in 31/4/1 (Q33(a)), 31/4/2 (Q33(a))

    A fuse in electric circuit is rated 4 A. Can it be used with an electric heater of rating 2 kW, 200 V ? Explain your answer.
    Show answer

    No; the heater draws 10 A, more than the 4 A rating, so the fuse would melt.

    No, a A fuse cannot be used. The heater draws A in normal working. The current rating of a fuse is the largest current its wire can carry without melting, and A is two and a half times the fuse's A rating, so the fuse wire would melt and break the circuit the moment the heater is switched on. A fuse rated just above A must be used instead.
    Step-by-step solution →
    OR
    Q33(b) 2 marks

    Also in 31/4/1 (Q33(b)), 31/4/2 (Q33(b))

    How is an electromagnet made ? Write any two ways by which the strength of electromagnet can be increased.
    Show answer

    Wind insulated copper wire as a solenoid over a soft iron core and pass current; strength rises with more current or more turns.

    An electromagnet is made by winding a large number of closely spaced turns of insulated copper wire, in the form of a solenoid, over a soft iron core, and passing an electric current through the coil from a battery through a plug key. While the current flows, the soft iron core is strongly magnetised and the whole arrangement behaves as a magnet with a north and a south pole; as soon as the current is switched off the core loses almost all of its magnetism. Two ways of increasing its strength: (i) increase the current flowing through the coil; (ii) increase the number of turns of the coil.
    Step-by-step solution →
  2. Q34 2 marks
    1. (a)State the law which gives the relation between the electric current flowing through a given conductor and the potential difference applied across it.
    2. (b)Draw V-I graph for a given conductor as per the law stated in above question (a).
    Show answer

    Ohm's law: at constant temperature is directly proportional to ; the – graph is a straight line through the origin.

    (a) The law is Ohm's law. It states that the potential difference across the ends of a given metallic conductor is directly proportional to the electric current flowing through it, provided its temperature and other physical conditions remain unchanged. In symbols, , so , where the constant of proportionality is the resistance of the conductor. (b) The graph of against - potential difference on the vertical axis, current on the horizontal axis - is a straight line passing through the origin, drawn in the figure in this solution. Its slope is constant and equals , the resistance of the conductor; for the line drawn there, .
    Step-by-step solution →

Questions 35–37 · 3 marks each

  1. Q35 3 marks

    Also in 31/4/1 (Q36)

    Explain the phenomenon of rainbow formation in the sky. Draw the labelled ray diagram in support of your explanation.
    Show answer

    A rainbow forms as droplets refract and disperse sunlight, reflect it internally and refract it again, with red outside and violet inside.

    A rainbow is a natural spectrum seen in the sky after a rain shower. It is produced by the tiny water droplets left suspended in the air, each of which acts like a small prism, and it is always seen in the direction opposite to the Sun, so the observer must stand with the Sun behind and the droplets in front. Three things happen to sunlight inside one droplet: (i) it is refracted as it passes from air into the water, and since water bends violet more than red the white light is dispersed into its colours; (ii) the dispersed light reaches the inner back surface of the droplet and is reflected internally, which turns it back towards the front of the drop; (iii) it is refracted again as it leaves the droplet into the air, and this second refraction spreads the colours further apart. Because red is returned at the larger angle, about to the incoming sunlight, and violet at a slightly smaller angle, the droplets that send red to the eye lie higher in the sky than those that send violet, so the bow appears with red on its outer edge and violet on its inner edge. The labelled ray diagram of a single droplet, showing refraction with dispersion, internal reflection and refraction with dispersion again, accompanies this answer.
    Step-by-step solution →
  2. Q36 3 marks

    Also in 31/4/1 (Q37), 31/4/2 (Q35)

    On the basis of the given circuit arrangement, answer the following questions :
    1. (a)What happens to the rod AB when the key K is closed and why ?
    2. (b)Name and state the rule that determines this behaviour of the rod AB in the above situation.
    A B S N − + K
    Show answer

    The rod carrying current B to A in the upward field is displaced sideways, to the left; Fleming's left-hand rule.

    (a) When K is closed a current flows through the rod AB, from end B to end A. The rod is then a current-carrying conductor lying across the magnetic field of the horseshoe magnet, which in the gap is directed vertically upwards because the N pole is below the rod and the S pole above it. A current-carrying conductor placed in a magnetic field experiences a mechanical force perpendicular both to the current and to the field, so the freely suspended rod is displaced: it swings horizontally, at right angles to its own length, towards the left. Taking the plug out of K stops the current, the force vanishes and the rod returns to rest. (b) The rule is Fleming's left-hand rule. Stretch the thumb, the forefinger and the central finger of the left hand so that all three are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the central finger points in the direction of the current, then the thumb points in the direction of the force acting on the conductor, that is, in the direction in which the rod moves.
    Step-by-step solution →
  3. Q37 3 marks
    A mirror used for rear-view of an automobile has a focal length 2.0 m. If a car is located at 8.0 m from the mirror -
    1. (a)Find out the position of the image of this car as seen in the mirror.
    2. (b)Draw the ray-diagram for image formation by the rear-view mirror.
    Show answer

    m: the image is 1.6 m behind the mirror, virtual, erect and diminished.

    (a) A mirror used for the rear view of an automobile is a convex mirror, so under the New Cartesian sign convention its focus lies behind the mirror and m, while the car stands in front of the mirror so m. From the mirror formula, , giving m. The image of the car is formed m **behind** the mirror. The magnification is , so the image is virtual, erect and one-fifth the size of the car, and it lies between the pole and the focus - the position a convex mirror always puts its image in, since . (b) The ray diagram is drawn in the figure in this solution. From the top of the car one ray is drawn parallel to the principal axis, which after reflection diverges as if coming from the focus behind the mirror, and a second ray is aimed at the centre of curvature , which strikes the mirror along the normal and is reflected back along its own path. The reflected rays themselves diverge and go on to the driver's eye; their backward extensions, drawn dashed behind the mirror, meet m from the pole, and the erect, diminished virtual image is drawn there.
    Step-by-step solution →

Question 38 · 4 marks

  1. Q38 4 marks

    Also in 31/4/1 (Q38), 31/4/2 (Q38)

    The above ray diagram is to show image formation by a reflecting telescope. Reflecting telescope revolutionized our way of looking into the sky. Reflecting telescopes employ large mirrors to gather and focus light rather than relying solely on lenses as we do in the refracting telescopes. These telescopes utilize precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where the telescope forms an image for observation.
    Parallel Light Rays from distant star Plane Mirror Curved Mirror Eye-piece
    1. (a)What kind of image of a star is seen by the observer in the eye-piece ?
    2. (b)What kind of mirror is used in this reflecting telescope ?
    3. (c)Explain with the reason, what kind of optical device (type of lens or mirror) is used at the eye-piece.
    4. (c)OR : What is the role of plane mirror in image formation by this telescope ?
    Show answer

    Virtual, magnified, inverted image; a concave mirror with a plane mirror; a convex lens as eye-piece; or the plane mirror redirects the light.

    (a) A virtual, magnified image, inverted with respect to the star. The curved mirror first forms a real, inverted image of the star at its focus, and the eye-piece, used as a magnifying glass on that image, gives the enlarged virtual image the observer actually sees. (b) A concave (converging) mirror - the large curved mirror that brings the parallel rays from a distant star to a real focus - together with a small plane mirror that turns the converging beam towards the eye-piece. (c) A convex (converging) lens is used at the eye-piece. It magnifies the image formed by the curved mirror: that small real image lies at or just within the focal length of the lens, so the lens acts as a magnifying glass and gives a much enlarged virtual image of it; a concave lens would only diminish the image, and a mirror there would send the light back into the tube instead of to the eye. OR (c) The plane mirror redirects (reflects) the light rays coming from the curved mirror towards the eye-piece. Held at in the path of the converging beam, it turns the beam through and brings the real image out through the side of the tube, so that the eye-piece and the observer's head do not block the starlight falling on the curved mirror; it forms no image of its own and does not change the size of the image.
    Step-by-step solution →

Question 39 · 5 marks

  1. Q39(a) 5 marks
    1. (i)Derive an expression for the equivalent resistance of three resistors connected in parallel with a battery as shown in figure.
    2. (ii)Find the values of the electric currents flowing through the resistors , and in the given electric circuit.
    R1 = 2 Ω R2 = 4 Ω R3 = 6 Ω X Y V + − + − 12 V K A − +
    Show answer

    The equivalent resistance obeys , and the three resistors carry A, A and A.

    (i) The three resistors bridge the same two points, so each has the same potential difference across it while the branch currents add: . With , , and this gives , and dividing right through by leaves . (ii) The whole V of the battery appears between X and Y, so every resistor has V across it: A through , A through and A through . Their sum, A, is what the ammeter reads, and it agrees with A, since here , that is .
    Step-by-step solution →
    OR
    Q39(b) 5 marks
    1. (i)Define electrical resistivity of a material.
    2. (ii)How will the resistivity and resistance of a conducting wire change if the length and area of cross-section of wire both are doubled ? Justify your answer.
    3. (iii)Calculate the electric current flowing through a resistor that produces J of heat every second.
    Show answer

    Resistivity stays the same and resistance is unchanged when length and area both double; the current in the resistor is A.

    (i) The electrical resistivity of a material is the resistance of a conductor of that material of unit length and unit area of cross-section; from it is , its SI unit is the ohm metre ( m), and it depends only on the material and its temperature. (ii) The resistivity does **not** change, because it is a property of the material and the material is the same. The resistance does not change either: . The justification is that doubling the length on its own would double while doubling the area on its own would halve it, and - equivalently, depends on the shape only through the ratio , which doubling both leaves unchanged. (iii) From , , so A.
    Step-by-step solution →

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