4. Carbon and its Compounds Class 10 NCERT Exemplar Solutions (CBSE 2026 Guide)

Class 10 Science Chapter 4: Carbon and its Compounds : NCERT Exemplar Solutions with Detailed Explanation

Chapter 4: Carbon and its Compounds

Multiple Choice Questions

1. Carbon exists in the atmosphere in the form of

(a) carbon monoxide only

(b) carbon monoxide in traces and carbon dioxide

(c) carbon dioxide only

(d) coal

Answer : (c) carbon dioxide only

[ Carbon exists in the atmosphere primarily in the form of carbon dioxide (). ]

2. Which of the following statements are usually correct for carbon compounds? These

(i) are good conductors of electricity

(ii) are poor conductors of electricity

(iii) have strong forces of attraction between their molecules

(iv) do not have strong forces of attraction between their molecules

(a) (i) and (iii) (b) (ii) and (iii) (c) (i) and (iv) (d) (ii) and (iv)

Answer : (d) (ii) and (iv)

[ Carbon compounds are generally poor conductors of electricity (ii) and do not have strong forces of attraction between their molecules (iv).]

3. A molecule of ammonia () has

(a) only single bonds (b) only double bonds (c) only triple bonds (d) two double bonds and one single bond

Answer : (a) only single bonds .

[ A molecule of ammonia () has only single bonds. ]

4. Buckminsterfullerene is an allotropic form of

(a) phosphorus (b) sulphur (c) carbon (d) tin

Answer : (c) carbon

[ Buckminsterfullerene is an allotropic form of carbon. ]

5. Which of the following are correct structural isomers of butane?

(a) (i) and (iii) (b) (ii) and (iv) (c) (i) and (ii) (d) (iii) and (iv)

Answer: (c) (i) and (ii)

[ Both structure (i) and (ii) share the same molecular formula() but have different structural arrangements.]

In the above given reaction, alkaline acts as

(a) reducing agent (b) oxidising agent (c) catalyst (d) dehydrating agent

Answer : (b) oxidising agent

[ In the given reaction:

Alkaline is acting as an oxidizing agent. ]

7. Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats. This is an example of

(a) Addition reaction (b) Substitution reaction (c) Displacement reaction (d) Oxidation reaction

Answer : (a) Addition reaction

[ The process described, where oils are treated with hydrogen in the presence of a catalyst (palladium or nickel) to form fats, is an example of an addition reaction. ]

8. In which of the following compounds, — OH is the functional group?

(a) Butanone (b) Butanol (c) Butanoic acid (d) Butanal

Answer : (b) Butanol

[ In the given options, the functional group —OH is present in the compound Butanol.]

9. The soap molecule has a

(a) hydrophilic head and a hydrophobic tail

(b) hydrophobic head and a hydrophilic tail

(c) hydrophobic head and a hydrophobic tail

(d) hydrophilic head and a hydrophilic tail

Answer : (a) hydrophilic head and a hydrophobic tail

[ The soap molecule has a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. ]

10. Which of the following is the correct representation of electron dot structure of nitrogen?

Answer : (d)

[ Each nitrogen atom shares 3 pairs of valence electrons to form a stable triple bond (), leaving one lone pair on each atom.]

11. Structural formula of ethyne is

Answer : (a)

[ Ethyne () is an alkyne containing a triple bond between two carbon atoms, with each carbon bonded to one hydrogen atom (). ]

12. Identify the unsaturated compounds from the following

(i) Propane (ii) Propene (iii) Propyne (iv) Chloropropane

(a) (i) and (ii) (b) (ii) and (iv) (c) (iii) and (iv) (d) (ii) and (iii)

Answer : (d) (ii) and (iii).

[ The unsaturated compounds are (ii) Propene and (iii) Propyne. ]

13. Chlorine reacts with saturated hydrocarbons at room temperature in the

(a) absence of sunlight (b) presence of sunlight (c) presence of water (d) presence of hydrochloric acid

Answer : (b) presence of sunlight.

[ Chlorine reacts with saturated hydrocarbons at room temperature in the presence of sunlight. The reaction is a substitution reaction known as free radical halogenation. ]

14. In the soap micelles

(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.

(c) both ionic end and carbon chain are in the interior of the cluster

(d) both ionic end and carbon chain are on the exterior of the cluster

Answer : (a) The ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

[In the formation of micelles, the hydrophobic tails (carbon chain) of soap molecules cluster in the interior, away from water, while the hydrophilic heads (ionic end) remain on the surface, interacting with water. ]

15. Pentane has the molecular formula . It has

(a) 5 covalent bonds (b) 12 covalent bonds (c) 16 covalent bonds (d) 17 covalent bonds

Answer : (c) 16 covalent bonds.

[ Pentane has the molecular formula C₅H₁₂

There are 4 C – C bonds and 12 C – H bonds

So, total covalent bonds = 4 + 12 = 16 ]

16. Structural formula of benzene is

Answer: Correct option (C)

[ Benzene () consists of six carbon atoms arranged in a ring with three alternating C–C single bonds and three C=C double bonds, where each carbon atom is bonded to one hydrogen atom.]

17. Ethanol reacts with sodium and forms two products. These are

(a) sodium ethanoate and hydrogen (b) sodium ethanoate and oxygen

(c) sodium ethoxide and hydrogen (d) sodium ethoxide and oxygen

Answer : (c) Sodium ethoxide

[ When ethanol () reacts with sodium (Na), it undergoes a reaction known as alcoholysis. The products of this reaction are sodium ethoxide () and hydrogen gas (). Therefore, the correct option is:

hydrogen]

18. The correct structural formula of butanoic acid is

Answer : (d)

[ Butanoic acid contains four carbon atoms with a terminal carboxylic acid group () ]

19. Vinegar is a solution of

(a) 50% – 60% acetic acid in alcohol (b) 5% – 8% acetic acid in alcohol

(c) 5% – 8% acetic acid in water (d) 50% – 60% acetic acid in water

Answer : (c) 5% – 8% acetic acid in water

[ Vinegar is a solution of 5% – 8% acetic acid in water. ]

20. Mineral acids are stronger acids than carboxylic acids because

(i) mineral acids are completely ionised (ii) carboxylic acids are completely ionised

(iii) mineral acids are partially ionised (iv) carboxylic acids are partially ionised

(a) (i) and (iv) (b) (ii) and (iii) (c) (i) and (ii) (d) (iii) and (iv)

Answer : (a) (i) and (iv).

[ Mineral acids are stronger acids than carboxylic acids because : (i) Mineral acids are completely ionized. (iv) Carboxylic acids are partially ionized. ]

21. Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of

(a) helium (b) neon (c) argon (d) krypton

Answer : (c) Argon

[ Carbon has electronic configuration 2.4 . By forming four covalent bonds, it completes 8 electrons in its outermost shell. This gives carbon the stable electronic configuration of Neon (2,8).]

22. The correct electron dot structure of a water molecule is

Answer: (c)

[ Oxygen shares one electron pair with each hydrogen atom, leaving two unshared lone pairs on oxygen so all atoms achieve stable outer shells. ]

23. Which of the following is not a straight chain hydrocarbon?

Answer: (d)

[ It is a branched-chain hydrocarbon because one carbon is attached to three other carbons. (a) , (b) and (c) are continuous straight chains. ]

24. Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii) (b) (ii) and (iii) (c) (ii) and (iv) (d) (iii) and (iv)

Answer: (c) (ii) and (iv)

[ The unsaturated hydrocarbons contain double () or triple () bonds, which are present in structures (ii) and (iv) ]

25. Which of the following does not belong to the same homologous series?

(a) (b) (c) (d)

Answer : (d) - Butene

[ The homologous series is a group of organic compounds that have the same functional group and share a similar chemical properties and successive members differ by - CH2 - . The reason is that it is an alkene (contains a double bond), while the others are alkanes (contain only single bonds). ]

26. The name of the compound is

(a) Propanal (b) Propanone (c) Ethanol (d) Ethanal

Answer: (a) Propanal

[ The compound CH₃–CH₂–CHO contains an aldehyde group (–CHO) .So, the name is Propanal.]

27. The heteroatoms present in are

(i) oxygen (ii) carbon (iii) hydrogen (iv) chlorine

(a) (i) and (ii) (b) (ii) and (iii)

(c) (iii) and (iv) (d) (i) and (iv)

Answer : (d) (i) and (iv).

[ The heteroatoms present in the given molecule are: (i) Oxygen (iv) Chlorine ]

28. Which of the following represents saponification reaction?

(a)

(b)

(c)

(d)

Answer : (d) .

[ Saponification is the reaction in which an ester reacts with a base (NaOH/KOH) to form salt of carboxylic acid (soap) and an alcohol.

The reaction is: ]

29. The first member of alkyne homologous series is

(a) ethyne (b) ethene (c) propyne (d) methane

Answer: (a) ethyne .

[ Alkynes are hydrocarbons containing a triple bond (C ≡ C).
The smallest possible alkyne has 2 carbon atoms, which is ethyne (C₂H₂).]

Short Answer Questions

30. Draw the electron dot structure of ethyne and also draw its structural formula.

Answer: The electron dot structure of ethyne :

Molecular formula:

Structural formula:

31. Write the names of the following compounds

Answer: (a) Pentanioc Acid ()

(b) Butyne ()

(d) Pentanol ()

32. Identify and name the functional groups present in the following compounds.

Answer: (a) Alcohol : → (Propanol)

(b) Carboxylic acid : → (Propanoic acid)

(d) Alkene : (Butene) → (Butene)

33. A compound X is formed by the reaction of a carboxylic acid and an alcohol in presence of a few drops of . The alcohol on oxidation with alkaline followed by acidification

gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.

Answer : (a) Carboxylic acid (Original):

Name: Ethanoic acid ()

Structure: Photo

(b) Alcohol:

Name: Ethanol ()

Structure: Photo

Name: Ethyl ethanoate ()

Structure: Photo

The chemical reaction are :

and

34. Why detergents are better cleansing agents than soaps? Explain.

Answer: Detergents are better cleansing agents than soaps because they work well in both soft water and hard water. Soaps react with calcium and magnesium salts present in hard water to form insoluble scum, reducing their cleansing action. Detergents do not form scum with hard water salts, so they produce more lather and clean more effectively.

35. Name the functional groups present in the following compounds

(a)

(b)

(c)

(d)

Answer: (a): Ketone ()

(b) : Carboxylic Acid ()

(d) : Alcohol ()

36. How is ethene prepared from ethanol? Give the reaction involved in it.

Answer: Ethene () is prepared from ethanol () by heating ethanol at 443 K in the presence of concentrated sulphuric acid (). In this process, a molecule of water is removed from ethanol (dehydration).

37. Intake of small quantity of methanol can be lethal. Comment.

Answer: Methanol is highly poisonous. In the body, it gets oxidised to methanoic acid (formic acid), which affects the nervous system and damages the optic nerves. Intake of even a small quantity of methanol can cause blindness and may even lead to death.

38. A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Answer : The gas evolved when ethanol reacts with sodium is hydrogen gas ().

The balanced chemical equation for the reaction is:

39. Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.

Answer: Concentrated sulphuric acid acts as a dehydrating agent in this reaction. It removes a molecule of water from ethanol to form ethene.

The balanced chemical equation for this reaction is:

40. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with

(a) chlorine (Group 17 of Periodic Table)

(b) oxgygen (Group 16 of Periodic Table)

Answer: (a) Carbon forms a compound with chlorine called Carbon tetrachloride → CCl₄

(b) Carbon forms a compound with oxygen called Carbon dioxide → CO₂

41. In electron dot structure, the valence shell electrons are represented by crosses or dots.

(a) The atomic number of chlorine is 17. Write its electronic configuration

(b) Draw the electron dot structure of chlorine molecule.

Answer: (a) The atomic number of chlorine (Cl) is 17.

Electronic configuration of chlorine (Cl) is 2.8.7 .

(b) The electron dot structure of chlorine molecule :

42. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Answer : Carbon exhibits a greater ability for catenation than silicon due to its smaller atomic size, which allows for stronger C-C bonds. Additionally, carbon's ability to form stable multiple bonds (double and triple bonds) enhances its catenation properties. Silicon, with its larger atomic size and weaker Si-Si bonds, shows less catenation capability.

43. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.

Answer: The test used to distinguish between ethane and ethene is:

Property	Ethane	Ethene
Reaction with bromine water	No change in colour	Bromine water gets decolourised
Test with alkaline KMnO₄	No change	Pink colour disappears
Type of reaction	Does not show addition reaction	Shows addition reaction

44. Match the reactions given in Column (A) with the names given in Column (B).

Column (A)	Column (B)
(a)	(i) Addition reaction
(b)	(ii) Substitution reaction
(c)	(iii) Neutralisation reaction
(d)	(iv) Esterification reaction

Answer : (a) → (iv) Esterification reaction

(b) → (i) Addition reaction

(d) → (iii) Neutralization reaction

45. Write the structural formulae of all the isomers of hexane.

Answer : The structure formula of isomers of hexane are :

(i) : n-hexane

(ii) : Isohexane (2-methylpentane)

(iii) : 3-methylpentane

(iv) : Neohexane (2,2-dimethylbutane)

(v) : 2,3 dimethylbutane

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46. What is the role of metal or reagents written on arrows in the given chemical reactions?

Answer: (a) Ni (Nickel) → Acts as a catalyst in the hydrogenation reaction. It helps in the addition of hydrogen () to the alkene.

(b) Conc. (Concentrated sulphuric acid) → Acts as a dehydrating catalyst in esterification. It helps in the formation of ester and removes water.

Long Answer Questions

47. A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write chemical equation of the reaction involved.

Answer: When ethanoic acid reacts with sodium hydrogencarbonate, sodium ethanoate (salt X) and carbon dioxide gas are formed.

The chemical reaction is:

Salt X: Sodium ethanoate (CH₃COONa)

Gas: Carbon dioxide (CO₂)

Activity to prove that the evolved gas is carbon dioxide:

(i) Take some ethanoic acid in a test tube.

(ii) Add sodium hydrogencarbonate to it.

(iii) A gas is evolved. Pass this gas through freshly prepared lime water using a delivery tube.

(iv) The lime water turns milky, proving that the gas evolved is carbon dioxide.

Chemical equation for lime water test:

The milkiness is due to the formation of calcium carbonate ().

Diagram of the apparatus:

Photo

48. (a) What are hydrocarbons? Give examples.

(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.

(c) What is a functional group? Give examples of four different functional groups.

Answer: (a) Hydrocarbons are carbon compounds which contain only carbon and hydrogen atoms.
Examples: Methane (CH₄), Ethane (C₂H₆)

(b) The structural difference between saturated and unsaturated hydrocarbons are :

Saturated hydrocarbons	Unsaturated hydrocarbons
Contain only single bonds between carbon atoms (C–C)	Contain at least one double or triple bond (C=C or C≡C)
General formula: (Alkane)	General formula: (alkenes), (alkynes)
Less reactive, do not show addition reactions easily	More reactive, show addition reactions
Examples: Ethane (C₂H₆), Propane (C₃H₈)	Examples: Ethene (C₂H₄), Ethyne (C₂H₂)

(c) Functional Group: A functional group is an atom or group of atoms that gives specific chemical properties to a compound.

(i) Alcohol group ( ):

Example: Ethanol ( ).

(ii) Halo-(Chloro/Bromo) Group ( - Cl / - Br ):

Example : Chloroethane (

(iii) Aldehyde ( ):

Example: Methanal ()

(iv) Ketone ():

Example: Acetone ()

(v) Carboxyl Group ( ):

Example: Acetic acid ().

49. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.

Answer: The reaction commonly used in the conversion of vegetable oils to fats is hydrogenation.

Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.

For example :

50. (a) Write the formula and draw electron dot structure of carbon tetrachloride.

(b) What is saponification? Write the reaction involved in this process.

Answer: (a) Carbon Tetrachloride (CCl₄):

Formula: CCl₄

Electron dot structure of CCl₄ :

(b) Saponification: The reaction in which an ester reacts with a base (NaOH or KOH) to form an alcohol and the salt of a carboxylic acid (soap) is called saponification.

The general reaction: Ester + NaOH → Alcohol + Sodium salt of carboxylic acid

The reaction involved in saponification is:

51. Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labeled diagram.

Answer: Take 1 mL ethanol and 1 mL acetic acid in a test tube. Add a few drops of concentrated sulphuric acid and warm the mixture in a water bath. After some time, a sweet smell is produced due to the formation of an ester called ethyl ethanoate.

The chemical Reaction:

52. A compound C (molecular formula,) reacts with Na-metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in presence of an acid forms a sweet smelling compound S (molecular formula, ) . On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Answer: The compound C = Ethanoic acid (CH₃COOH)

Reaction with Na gives salt:
R = Sodium ethanoate (CH₃COONa)

Alcohol A must be Methanol (CH₃OH) to form ester C₃H₆O₂ :
A = Methanol (CH₃OH)
S = Methyl ethanoate (CH₃COOCH₃)

(i) With sodium:
CH₃COOH + Na → CH₃COONa + H₂

(ii) With alcohol (esterification):
CH₃COOH + CH₃OH → CH₃COOCH₃ + H₂O

(iii) With NaOH:
CH₃COOH + NaOH → CH₃COONa + H₂O

(iv) Saponification:
CH₃COOCH₃ + NaOH → CH₃COONa + CH₃OH

53. Look at Figure 4.1 and answer the following questions

Fig. 4.1

(a) What change would you observe in the calcium hydroxide solution taken in tube B?

(b) Write the reaction involved in test tubes A and B respectively.

(c) If ethanol is given instead of ethanoic acid, would you expect the same change?

(d) How can a solution of lime water be prepared in the laboratory?

Answer: (a) In tube B, which contains lime water (a calcium hydroxide solution), the solution turns milky. This occurs because the carbon dioxide gas produced in test tube A reacts with the calcium hydroxide in tube B, forming calcium carbonate, which is insoluble in water and causes the milky appearance.

(b) In test tube A, the reaction involves ethanoic acid () reacting with sodium carbonate (). The reaction produces sodium ethanoate (), carbon dioxide (), and water ().
The chemical equation is:

In test tube B, the carbon dioxide produced in test tube A reacts with the lime water (calcium hydroxide,) in test tube B, forming calcium carbonate (), which is insoluble in water and gives a milky appearance. The chemical equation is:

(c) No, we would not expect the same change if ethanol () is used instead of ethanoic acid (). Ethanol does not react with sodium carbonate () to produce carbon dioxide. Therefore, no carbon dioxide would be released and there would be no reaction in tube B. The lime water would remain clear.

(d) Lime water is prepared by adding water to quicklime (calcium oxide). Quicklime reacts with water to form calcium hydroxide. The clear solution obtained after filtering is called lime water.

The chemical reaction is:

54. How would you bring about the following conversions? Name the process and write the reaction involved.

(a) ethanol to ethene. (b) propanol to propanoic acid.

Write the reactions.

Answer: (a) Dehydration: When ethanol is heated to 443 K with excess concentrated sulphuric acid, ethene and water are produced.

(b) Oxidation : When propanol is heated with alkaline potassium permanganate or acidified potassium dichromate, it produces propanoic acid.

55. Draw the possible isomers of the compound with molecular formula and also give their electron dot structures.

Answer: The compound with molecular formula has the following possible isomers:

(i) Propanal

Structural formula: CH₃–CH₂–CHO

Electron dot structures: Photo

(ii) Propanone

Structural formula: CH₃–CO–CH₃

Electron dot structures:

56. Explain the given reactions with the examples

(a) Hydrogenation reaction (b) Oxidation reaction (c) Substitution reaction (d) Saponification reaction (e) Combustion reaction

Answer: (a) Hydrogenation reaction: Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as nickel or palladium to form saturated hydrocarbons. This process is called a hydrogenation reaction.

Example: Hydrogenation of ethene (C₂H₄) to ethane (C₂H₆) in the presence of a nickel catalyst:

(b) Oxidation Reaction: A reaction in which oxygen is added to a substance or hydrogen is removed from it is called an oxidation reaction. Alkaline potassium permanganate or acidified potassium dichromate oxidise alcohols to acids by adding oxygen to the starting material. Therefore, they are known as oxidising agents.

Example: Oxidation of ethanol () to acetic acid ():

(c) Substitution reaction: A reaction in which one or more atoms of a compound are replaced by other atoms without changing the basic structure of the compound is called a substitution reaction.

For example, methane reacts with chlorine to form chloromethane and hydrogen chloride .

(d) Saponification Reaction: The reaction in which an ester reacts with a base (NaOH or KOH) to form an alcohol and the salt of a carboxylic acid (soap) is called saponification reaction.

The general reaction: Ester + NaOH → Alcohol + Sodium salt of carboxylic acid.

Example : The reaction of esters with NaOH to produce ethanol and Sodium ethanoate (soap).

(e) Combustion Reaction: The process of burning a carbon compound (hydrocarbon) in the presence of sufficient oxygen to produce carbon dioxide, water, heat, and light.

Example: Methane reacts with oxygen to produce carbon dioxide, water, and a large amount of heat.

heat and light

57. An organic compound A on heating with concentrated forms a compound B which on addition of one mole of hydrogen in presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of and 3 moles of . Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Answer: A = Ethanol () ; B = Ethene () ; C = Ethane ()

Formation of B from A (Dehydration):

Addition of one mole of hydrogen to B (Hydrogenation):

Combustion of one mole of C: