Class 10 Science · Chapter 4

Carbon and its Compounds

201 Class 10 Science questions on Carbon and its Compounds 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 2 of 11

1. Q21 NCERT · Intext Questions (Page 68)
   Draw the structures for the ​following ​compounds.

   1. (i)​Ethanoic acid
   2. (ii)Bromopentane*
   3. (iii)​Butanone
   4. (iv)​Hexanal. *Are ​structural isomers ​possible for bromopentane?
   Show answer

   Structures drawn for the four compounds; bromopentane does have structural isomers (bromine on carbon 1, 2 or 3, or a branched chain).

   (i) Ethanoic acid: ${\text{CH}}_3-\text{COOH}$ — a ${\text{CH}}_3$ carbon joined to a carbon that carries a doubly bonded oxygen and an $-\text{OH}$ group. (ii) Bromopentane: ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{Br}$ — a five-carbon chain in which one hydrogen is replaced by bromine (drawn with Br on an end carbon), ${\text{C}}_5{\text{H}}_{11}\text{Br}$. (iii) Butanone: ${\text{CH}}_3-\text{CO}-{\text{CH}}_2-{\text{CH}}_3$ — a four-carbon chain with the ketone $\text{C}=\text{O}$ on the second carbon. (iv) Hexanal: ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{CHO}$ — a six-carbon chain with the aldehyde group $-\text{CHO}$ at the end. *Yes, structural isomers are possible for bromopentane: the bromine atom can be attached to carbon 1, 2 or 3 of the straight chain (1-bromopentane, 2-bromopentane, 3-bromopentane), and the carbon chain itself can be branched (for example 1-bromo-2-methylbutane); all of them have the same molecular formula ${\text{C}}_5{\text{H}}_{11}\text{Br}$.

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2. Q22 NCERT · Intext Questions (Page 68)
   How would you ​name the following compounds?

   1. (i)${\text{CH}}_3-{\text{CH}}_2-\text{Br}$
   2. (ii)The second structure drawn in the ​figure.
   3. (iii)​The third ​structure ​drawn ​in the figure.

   Show answer

   (i) Bromoethane, (ii) methanal, (iii) hexyne (hex-1-yne).

   (i) Bromoethane — two carbons (ethane) with a bromine atom in place of one hydrogen. (ii) Methanal — one carbon carrying the aldehyde group $-\text{CHO}$ (commonly called formaldehyde). (iii) Hexyne — a six-carbon chain with a triple bond, ${\text{CH}}_3-{\text{CH}}_2-{\text{CH}}_2-{\text{CH}}_2-\text{C}\equiv \text{CH}$; since the triple bond is on the first carbon, it is hex-1-yne.

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3. Q23 NCERT · Intext Questions (Page 71)
   Why ​is ​the ​conversion ​of ethanol to ethanoic ​acid ​an oxidation reaction?
   Show answer

   Ethanol gains one oxygen atom and loses two hydrogen atoms on becoming ethanoic acid, and gain of oxygen is oxidation.

   Because in this conversion ethanol gains oxygen (and loses hydrogen): ${\text{CH}}_3{\text{CH}}_2\text{OH}$ (${\text{C}}_2{\text{H}}_6\text{O}$) becomes ${\text{CH}}_3\text{COOH}$ (${\text{C}}_2{\text{H}}_4{\text{O}}_2$) — one oxygen atom is added and two hydrogen atoms are removed. Addition of oxygen to a substance (or removal of hydrogen from it) is oxidation, so ethanol is oxidised to ethanoic acid. The oxygen is supplied by an oxidising agent, alkaline potassium permanganate or acidified potassium dichromate, on heating: ${\text{CH}}_3{\text{CH}}_2\text{OH}+2[\text{O}]\to {\text{CH}}_3\text{COOH}+{\text{H}}_2\text{O}$.

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4. Q24 NCERT · Intext Questions (Page 71)
   A mixture of oxygen ​and ​ethyne is burnt for welding. Can ​you tell why a ​mixture ​of ethyne and air is not ​used?
   Show answer

   In air ethyne burns incompletely with a cooler, sooty flame; in pure oxygen it burns completely with a very hot flame that melts metals.

   Ethyne is an unsaturated hydrocarbon with a high proportion of carbon, and its complete combustion needs a large amount of oxygen: $2{\text{C}}_2{\text{H}}_2+5{\text{O}}_2\to 4{\text{CO}}_2+2{\text{H}}_2\text{O}+\text{heat and light}$. Air contains only about one-fifth oxygen (the rest is mostly nitrogen), so in air ethyne burns incompletely, giving a yellow, sooty flame that produces much less heat, while the nitrogen absorbs heat and cools the flame further; the soot would also spoil the metal being welded. In pure oxygen ethyne burns completely with a clean, extremely hot flame (about $3000{}^{\circ }\text{C}$), which is what is needed to melt metals for welding. That is why a mixture of ethyne and oxygen, and not ethyne and air, is used.

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5. Q25 NCERT · Intext Questions (Page 74)
   How ​would you ​distinguish experimentally between ​an ​alcohol ​and a carboxylic ​acid?
   Show answer

   Add sodium hydrogencarbonate: the carboxylic acid fizzes, giving carbon dioxide that turns lime water milky, but the alcohol does not.

   Add a small amount of sodium hydrogencarbonate (or sodium carbonate) to a little of each liquid. The carboxylic acid reacts with brisk effervescence, giving off carbon dioxide that turns lime water milky — ${\text{CH}}_3\text{COOH}+{\text{NaHCO}}_3\to {\text{CH}}_3\text{COONa}+{\text{H}}_2\text{O}+{\text{CO}}_2$ — whereas the alcohol gives no reaction and no gas. As a second test, a carboxylic acid turns blue litmus red while an alcohol has no effect on litmus. (Reaction with sodium metal cannot be used, because both an alcohol and a carboxylic acid give hydrogen with sodium.)

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6. Q26 NCERT · Intext Questions (Page 74)
   What are oxidising agents?
   Show answer

   Oxidising agents are substances that add oxygen to, or remove hydrogen from, other substances, and are themselves reduced.

   Oxidising agents are substances that are capable of adding oxygen to other substances (or of removing hydrogen from them), that is, substances that oxidise other substances and are themselves reduced in the process. Examples: alkaline potassium permanganate (${\text{KMnO}}_4$) and acidified potassium dichromate (${\text{K}}_2{\text{Cr}}_2{\text{O}}_7$), which add oxygen to ethanol and oxidise it to ethanoic acid — ${\text{CH}}_3{\text{CH}}_2\text{OH}\stackrel{\text{alkaline }{\text{KMnO}}_4+\text{heat}}{\to }{\text{CH}}_3\text{COOH}$. Oxygen itself is also an oxidising agent, as in combustion.

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7. Q27 NCERT · Intext Questions (Page 76)
   Would ​you ​be ​able ​to check if water is hard by using a ​detergent?
   Show answer

   No: a detergent lathers equally well in hard and soft water, so only a soap solution can show hardness.

   No. Hardness of water is detected by the behaviour of soap: in hard water soap reacts with the dissolved calcium and magnesium salts to form an insoluble white curdy precipitate (scum) and gives very little lather. A detergent does not form insoluble precipitates with calcium and magnesium ions — it lathers equally well in hard and in soft water and forms no scum — so with a detergent there is no visible difference between hard and soft water, and it cannot be used to check whether water is hard. A soap solution must be used for this test.

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8. Q28 NCERT · Intext Questions (Page 76)
   People use a variety of methods to wash clothes. Usually after adding the ​soap, they ‘beat’ the clothes on a ​stone, ​or beat it with a ​paddle, scrub with a brush or ​the mixture ​is agitated in a washing ​machine. Why is agitation necessary to get clean ​clothes?
   Show answer

   Soap only loosens the dirt; agitation pulls the dirt-laden micelles off the fibres and disperses them in water so rinsing can remove them.

   Most dirt on clothes is oily and is held on the fibres of the cloth. Soap molecules attach their hydrocarbon tails to this oily dirt and form micelles around it with their ionic ends facing the water, so that the dirt can be carried away in water as an emulsion. But soap by itself only loosens the dirt — the micelles containing the dirt are still attached to the fibres. Agitation (beating, scrubbing or the tumbling of a washing machine) supplies the mechanical force needed to break the oily dirt into small droplets that the micelles can surround, to pull the dirt-laden micelles away from the fibres, and to disperse them in the water. The suspended dirt is then removed by rinsing. Without agitation most of the dirt would stay on the cloth even after soap had been added.

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9. Q29 Exemplar · Multiple Choice Questions
   Carbon exists ​in the atmosphere ​in ​the ​form of

   1. (a)Carbon monoxide only
   2. (b)Carbon monoxide in traces and carbon dioxide
   3. (c)Carbon dioxide only
   4. (d)Coal
   Show answer

   (b) Carbon monoxide in traces and carbon dioxide

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10. Q30 Exemplar · Multiple Choice Questions
    Which ​of the following ​statements ​are usually correct ​for carbon compounds? ​These

    1. (i)are good conductors of ​electricity
    2. (ii)are poor conductors of electricity
    3. (iii)​have strong forces of attraction between ​their molecules
    4. (iv)do not have strong forces of attraction between their molecules

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

    (d) (ii) and (iv)

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11. Q31 Exemplar · Multiple Choice Questions
    A molecule ​of ammonia ​(${\text{NH}}_3$) ​has

    1. (a)Only single bonds
    2. (b)Only double bonds
    3. (c)Only triple bonds
    4. (d)Two double bonds and one single bond
    Show answer

    (a) Only single bonds

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12. Q32 Exemplar · Multiple Choice Questions
    Buckminsterfullerene is ​an ​allotropic ​form ​of

    1. (a)Phosphorus
    2. (b)Sulphur
    3. (c)Carbon
    4. (d)Tin
    Show answer

    (c) Carbon

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13. Q33 Exemplar · Multiple Choice Questions
    Which of the ​following are ​correct structural isomers ​of butane? ​The four structures (i), (ii), ​(iii) and (iv) are shown in ​the figure.

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

    (c) (i) and (ii)

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14. Q34 Exemplar · Multiple Choice Questions
    In ​the reaction ${\text{CH}}_3-{\text{CH}}_2-\text{OH}\stackrel{\text{alkaline }{\text{KMnO}}_4+\text{Heat}}{\to }{\text{CH}}_3-\text{COOH}$, ​alkaline ${\text{KMnO}}_4$ acts as

    1. (a)Reducing agent
    2. (b)Oxidising agent
    3. (c)Catalyst
    4. (d)Dehydrating agent
    Show answer

    (b) Oxidising agent

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15. Q35 Exemplar · Multiple Choice Questions
    Oils ​on treating ​with hydrogen in the ​presence of ​palladium or nickel catalyst form fats. This is ​an ​example of

    1. (a)Addition reaction
    2. (b)Substitution reaction
    3. (c)Displacement reaction
    4. (d)Oxidation reaction
    Show answer

    (a) Addition reaction

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16. Q36 Exemplar · Multiple Choice Questions
    In ​which ​of ​the ​following ​compounds, $-\text{OH}$ is ​the functional ​group?

    1. (a)Butanone
    2. (b)Butanol
    3. (c)Butanoic acid
    4. (d)Butanal
    Show answer

    (b) Butanol

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17. Q37 Exemplar · Multiple Choice Questions
    The soap molecule has a

    1. (a)Hydrophilic head and a hydrophobic tail
    2. (b)Hydrophobic head and a hydrophilic tail
    3. (c)Hydrophobic head and a hydrophobic tail
    4. (d)Hydrophilic head and a hydrophilic tail
    Show answer

    (a) Hydrophilic head and a hydrophobic tail

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18. Q38 Exemplar · Multiple Choice Questions
    Which ​of the following is ​the correct ​representation ​of electron dot structure of nitrogen? ​The four structures ​are ​shown in ​the figure.

    1. (a)One shared pair of dots between the two nitrogen atoms, with two further pairs on each atom
    2. (b)Two shared pairs between the atoms, with one lone pair and one single dot on each atom
    3. (c)Three dots between the atoms, two pairs on the left atom, and one pair and one single dot on the right atom
    4. (d)Three shared pairs between the atoms, with one lone pair on each atom
    Show answer

    (d) Three shared pairs between the atoms, with one lone pair on each atom

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19. Q39 Exemplar · Multiple Choice Questions
    Structural formula of ethyne is

    1. (a)$\text{H}-\text{C}\equiv \text{C}-\text{H}$
    2. (b)${\text{H}}_3-\text{C}\equiv \text{C}-\text{H}$
    3. (c)${\text{H}}_2\text{C}={\text{CH}}_2$, drawn with two hydrogen atoms on each carbon and a double bond between them
    4. (d)${\text{H}}_3\text{C}-{\text{CH}}_3$, drawn with three hydrogen atoms on each carbon and a single bond between them
    Show answer

    (a) $\text{H}-\text{C}\equiv \text{C}-\text{H}$

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20. Q40 Exemplar · Multiple Choice Questions
    Identify ​the unsaturated compounds ​from the ​following

    1. (i)​Propane
    2. (ii)​Propene
    3. (iii)​Propyne
    4. (iv)Chloropropane

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

    (d) (ii) and (iii)

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