Class 10 Science · Chapter 1

Chemical Reactions and Equations

201 Class 10 Science questions on Chemical Reactions and Equations from the NCERT textbook, NCERT Exemplar and CBSE board papers 2024–2026, each with its answer and a step-by-step solution.

CBSE Class 10 Science previous year papers, with answers →

Questions · page 5 of 11

1. Q81 CBSE 2026
   ${{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6}_{(\mathrm{aq})}+6{{\mathrm{O}}_2}_{(\mathrm{g})}⟶6{\mathrm{C}{\mathrm{O}}_2}_{(\mathrm{g})}+6{{\mathrm{H}}_2\mathrm{O}}_{(l)}$ 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 →
2. Q82 CBSE 2026
   On ​heating ​ferrous ​sulphate ​crystals, one would ​get :

   1. (a)Sweet smell
   2. (b)Rotten egg smell
   3. (c)Characteristic smell of burning sulphur
   4. (d)No smell
   Show answer

   (c) Characteristic smell of burning sulphur

   Step-by-step solution →
3. Q83 CBSE 2026
   On heating ​lead ​nitrate ​crystals, ​one ​would get ​:

   1. (a)yellow fumes
   2. (b)rotten egg smell
   3. (c)burning smell of sulphur
   4. (d)brown fumes
   Show answer

   (d) brown fumes

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4. Q84 CBSE 2026
   Which of the ​following compounds ​is formed on ​heating limestone with the release ​of ${\text{CO}}_2$ ​gas ​?

   1. (a)${\text{Ca(OH)}}_2$
   2. (b)${\text{CaCO}}_3$
   3. (c)$\text{CaO}$
   4. (d)${\text{CaCl}}_2$
   Show answer

   (c) $\text{CaO}$

   Step-by-step solution →
5. Q85 CBSE 2026
   Electrolysis ​of water is an ​example ​of ​:

   1. (a)thermal decomposition reaction
   2. (b)photochemical decomposition reaction
   3. (c)double-displacement reaction
   4. (d)electrolytic decomposition reaction
   Show answer

   (d) electrolytic decomposition reaction

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6. Q86 CBSE 2026
   The gases ​evolved ​on heating lead ​(II) ​nitrate ​crystals ​are ​:

   1. (a)$\text{NO}$ and ${\text{O}}_2$
   2. (b)${\text{N}}_2$ and ${\text{NO}}_2$
   3. (c)${\text{NO}}_2$ and ${\text{H}}_2$
   4. (d)${\text{NO}}_2$ and ${\text{O}}_2$
   Show answer

   (d) ${\text{NO}}_2$ and ${\text{O}}_2$

   Step-by-step solution →
7. Q87 CBSE 2026
   When ferrous sulphate crystals ​are heated in ​a ​test ​tube, we observe that :

   1. (a)A colourless gas with no smell is evolved.
   2. (b)A brown gas is evolved.
   3. (c)The green colour of the salt fades and a gas with the smell of burning sulphur is evolved.
   4. (d)The green colour of the salt fades and no gas is evolved.
   Show answer

   (c) The green colour of the salt fades and a gas with the smell of burning sulphur is evolved.

   Step-by-step solution →
8. Q88 CBSE 2026
   Which ​of the ​following are ​decomposition reactions ​?

   1. (i)$2{\text{KClO}}_3⟶2\text{KCl}+3{\text{O}}_2$
   2. (ii)$\text{MgO}+{\text{H}}_2\text{O}⟶{\text{Mg(OH)}}_2$
   3. (iii)$2{\text{H}}_2\text{O}⟶{\text{H}}_2+{\text{O}}_2$
   4. (iv)$\text{Zn}+{\text{CuSO}}_4⟶{\text{ZnSO}}_4+\text{Cu}$ Options ​:

   1. (a)(i) and (ii)
   2. (b)(iii) and (iv)
   3. (c)(i) and (iii)
   4. (d)(ii) and (iv)
   Show answer

   (c) (i) and (iii)

   Step-by-step solution →
9. Q89 CBSE 2026
   In ​the ​following equation $x\text{KI}+{\text{H}}_2{\text{O}}_2⟶{\text{I}}_2+y\text{KOH}$ $x$ and $y$ ​respectively ​are ​:

   1. (a)2, 2
   2. (b)1, 2
   3. (c)2, 1
   4. (d)1, 1
   Show answer

   (a) 2, 2

   Step-by-step solution →
10. Q90 CBSE 2026
    Which of the ​following ​are exothermic processes ? I. ​The decomposition of ​vegetable ​matter into compost II. Dilution of an acid III. Evaporation of water IV. ​Sublimation of camphor Options :

    1. (a)I and II
    2. (b)II and III
    3. (c)I and IV
    4. (d)III and IV
    Show answer

    (a) I and II

    Step-by-step solution →
11. Q91 CBSE 2026
    Which of ​the ​following statements about the given reaction ​are correct ​? $${\text{MnO}}_2+4\text{HCl}⟶{\text{MnCl}}_2+{\text{Cl}}_2+2{\text{H}}_2\text{O}$$

    1. (i)${\text{MnO}}_2$ is getting reduced.
    2. (ii)$\text{HCl}$ is getting oxidised.
    3. (iii)${\text{MnO}}_2$ acts as an ​oxidising agent.
    4. (iv)${\text{MnO}}_2$ acts as a reducing agent.

    1. (a)(i), (ii) and (iii)
    2. (b)(iii) and (iv)
    3. (c)(i), (ii) and (iv)
    4. (d)(ii) and (iv)
    Show answer

    (a) (i), (ii) and (iii)

    Step-by-step solution →
12. Q92 CBSE 2026
    In the question two statements ​are ​given – one labelled ​as Assertion (A) and ​other labelled as Reason (R). Answer this question selecting the ​appropriate option ​from (a), (b), (c) and (d) given below :

    Assertion (A): Reaction of quick lime with water is an exothermic reaction.

    Reason (R): A large amount of heat is evolved on the reaction of quick lime and water.

    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 →
13. Q93 CBSE 2026
    For ​Question number 24, two statements are given — ​one ​labelled ​as Assertion (A) and the other ​labelled as Reason (R). Select ​the correct answer to this question from ​the codes (a), (b), (c) and (d) ​as given below.

    Assertion (A): Burning of natural gas is an endothermic reaction.

    Reason (R): Methane gas reacts with oxygen to produce ${\text{CO}}_2$ and ${\text{H}}_2\text{O}$.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of 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

    (d) Assertion (A) is false, but Reason (R) is true.

    Step-by-step solution →
14. Q94 CBSE 2026
    For Question number 24, ​two ​statements ​are given — one labelled as ​Assertion (A) and the other labelled ​as Reason (R). Select the correct answer to this question from the codes (a), (b), (c) ​and (d) as ​given ​below.

    Assertion (A): Fat/oil-containing food items become rancid if they are kept in air for a long time.

    Reason (R): Oils and fats present in food items undergo slow oxidation in air.

    1. (a)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
    2. (b)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of 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 Assertion (A).

    Step-by-step solution →
15. Q95 CBSE 2026
    Answer ​the ​following :

    1. (a)Why should chemical equations be balanced ​?
    2. (b)Name ​the ​oxidising ​and reducing agent ​in the following equation : $4\text{Na}+{\text{O}}_2⟶2{\text{Na}}_2\text{O}$
    Show answer

    Equations are balanced because mass is conserved; oxygen is the oxidising agent and sodium is the reducing agent.

    (a) Chemical equations should be balanced because of the law of conservation of mass: mass can neither be created nor destroyed in a chemical reaction, so the number of atoms of each element, and the total mass, must be the same in the products as in the reactants. (b) Oxidising agent: oxygen, ${\text{O}}_2$. Reducing agent: sodium, $\text{Na}$. Sodium gains oxygen and is oxidised, so it is the reducing agent; oxygen oxidises sodium and is itself reduced, so it is the oxidising agent.

    Step-by-step solution →
16. Q96 CBSE 2026
    Account ​for the ​following :

    1. (a)White silver ​chloride turns grey when exposed to ​sunlight.
    2. (b)Lead (II) nitrate ​on heating releases brown fumes.
    3. (c)​Bags of oil and ​fat containing food items are ​flushed with nitrogen gas.
    Show answer

    Light decomposes silver chloride to grey silver; heated lead(II) nitrate gives brown ${\text{NO}}_2$; nitrogen keeps oxygen away from fatty food, preventing rancidity.

    (a) Sunlight decomposes silver chloride into grey, finely divided metallic silver and chlorine gas, so the white solid darkens. It is a photolytic (photochemical) decomposition reaction: $2\text{AgCl}(s)\stackrel{\text{sunlight}}{\to }2\text{Ag}(s)+{\text{Cl}}_2(g)$. (b) On heating, lead(II) nitrate decomposes into yellow lead(II) oxide, reddish-brown nitrogen dioxide and oxygen; the brown fume is the nitrogen dioxide. It is a thermal decomposition reaction: $2{\text{Pb(NO}}_3{\text{)}}_2(s)\stackrel{\Delta }{\to }2\text{PbO}(s)+4{\text{NO}}_2(g)+{\text{O}}_2(g)$. (c) Oils and fats are oxidised by the oxygen of the air and turn rancid. Nitrogen is unreactive, so flushing the bag with it drives the air out and leaves no oxygen inside; the oxidation cannot start and the food stays fresh. Here no reaction takes place — the nitrogen is used to prevent one.

    Step-by-step solution →
17. Q97 CBSE 2026
    Answer the following ​:

    1. (a)Identify the substance oxidized ​and the substance reduced in the following reaction : $4\mathrm{Na}+{\mathrm{O}}_2⟶2\mathrm{N}{\mathrm{a}}_2\mathrm{O}$
    2. (b)What type of reaction occurs when Lead (II) nitrate ​solution is mixed with potassium ​iodide solution ​?
    3. (c)Why is ​silver chloride stored in dark coloured bottles ​?
    Show answer

    Sodium is oxidized and oxygen reduced; the lead nitrate and potassium iodide reaction is double displacement; dark bottles stop light decomposing silver chloride.

    (a) Sodium is the substance oxidized and oxygen is the substance reduced. Sodium goes from an oxidation number of $0$ in the free metal to $+1$ in $\mathrm{N}{\mathrm{a}}_2\mathrm{O}$, a rise of one, losing one electron per atom, so it is oxidized and is the reducing agent. Oxygen goes from $0$ in ${\mathrm{O}}_2$ to $-2$ in $\mathrm{N}{\mathrm{a}}_2\mathrm{O}$, a fall of two, gaining two electrons per atom, so it is reduced and is the oxidising agent. (b) It is a double displacement reaction: the two solutions exchange their ions. Because the new pair $\mathrm{Pb}{\mathrm{I}}_2$ is insoluble and separates as a yellow solid, the same reaction is also called a precipitation reaction. $\mathrm{Pb}(\mathrm{N}{\mathrm{O}}_3{)}_2(aq)+2\mathrm{KI}(aq)⟶\mathrm{Pb}{\mathrm{I}}_2(s)+2\mathrm{KN}{\mathrm{O}}_3(aq)$ (c) Silver chloride is decomposed by light. Sunlight splits it into finely divided grey silver and chlorine gas, $2\mathrm{AgCl}\stackrel{\text{sunlight}}{\to }2\mathrm{Ag}+\mathrm{C}{\mathrm{l}}_2$, so a sample kept in a clear bottle slowly turns grey and is spoilt. A dark coloured bottle keeps the light out and prevents this photolytic decomposition.

    Step-by-step solution →
18. Q98 CBSE 2026
    1. (a)Name the substance ​oxidised and ​reduced in the ​following reaction ​: $\text{ZnO}+\text{C}⟶\text{Zn}+\text{CO}$
    2. (b)​Balance the following chemical reaction : $\text{Pb}({\text{NO}}_3{)}_2+\text{KI}⟶{\text{PbI}}_2+{\text{KNO}}_3$
    3. (c)Give one example ​each of electrolytic ​decomposition and decomposition by sunlight.
    Show answer

    Carbon is oxidised, zinc oxide reduced; the equation needs $2\text{KI}$ and $2{\text{KNO}}_3$; examples are electrolysis of water and silver chloride in sunlight.

    (a) Carbon ($\text{C}$) is oxidised to $\text{CO}$, and zinc oxide ($\text{ZnO}$) is reduced to $\text{Zn}$. (b) $\text{Pb}({\text{NO}}_3{)}_2+2\text{KI}⟶{\text{PbI}}_2+2{\text{KNO}}_3$ (c) Electrolytic decomposition: $2{\text{H}}_2\text{O}(l)\stackrel{\text{electric current}}{\to }2{\text{H}}_2(g)+{\text{O}}_2(g)$; decomposition by sunlight: $2\text{AgCl}(s)\stackrel{\text{sunlight}}{\to }2\text{Ag}(s)+{\text{Cl}}_2(g)$.

    Step-by-step solution →
19. Q99 CBSE 2026
    What happens when :

    1. (a)An iron ​nail is dipped in copper (II) sulphate solution ?
    2. (b)​Potassium iodide solution is mixed with ​lead ​nitrate ​solution ?
    3. (c)​Silver chloride is exposed to sunlight ? Write balanced chemical equations ​to support your answer.
    Show answer

    The iron nail gets a copper coating, lead iodide forms as a yellow precipitate, and white silver chloride turns grey in sunlight.

    (a) Iron displaces copper from copper(II) sulphate solution: the nail gets a reddish-brown coating of copper, and the blue colour of the solution fades to pale green (displacement reaction). $\text{Fe}(s)+{\text{CuSO}}_4(aq)⟶{\text{FeSO}}_4(aq)+\text{Cu}(s)$ (b) A yellow precipitate of lead iodide forms (double displacement, or precipitation, reaction). $\text{Pb}({\text{NO}}_3{)}_2(aq)+2\text{KI}(aq)⟶{\text{PbI}}_2(s)+2{\text{KNO}}_3(aq)$ (c) White silver chloride turns grey as sunlight decomposes it into silver and chlorine gas (decomposition by light). $2\text{AgCl}(s)\stackrel{\text{sunlight}}{\to }2\text{Ag}(s)+{\text{Cl}}_2(g)$

    Step-by-step solution →
20. Q100 CBSE 2026
    2 g of ​green coloured ​crystals of ferrous sulphate are heated in a dry ​boiling tube. Name the type ​of chemical reaction ​taking place. Write ​the balanced ​chemical equation for the reaction. Is this ​an exothermic or an endothermic reaction ?
    Show answer

    It is a thermal decomposition, $2{\text{FeSO}}_4\stackrel{\text{heat}}{\to }{\text{Fe}}_2{\text{O}}_3+{\text{SO}}_2+{\text{SO}}_3$, and it is endothermic because heat must be absorbed continuously.

    Type of reaction: thermal decomposition (a single reactant breaks down on heating). Balanced equation: $2{\text{FeSO}}_4\text{(s)}\stackrel{\text{heat}}{\to }{\text{Fe}}_2{\text{O}}_3\text{(s)}+{\text{SO}}_2\text{(g)}+{\text{SO}}_3\text{(g)}$; the green crystals, ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}$, first lose their water of crystallisation. Heat change: endothermic, because heat must be absorbed all the time for the ferrous sulphate to decompose.

    Step-by-step solution →