Chapter 4: Carbon and its Compounds

Important questions — the ones the board asked most (20)

1. Q1Long answer5 marksAsked: 2024

   34. (a) (i) Give reason why carbon can neither form C4+ cations nor C4- anions but form covalent compounds. (ii) What is homologous series of carbon compound ? Write the molecular formula of any two consecutive members of homologous series of aldehydes. (iii) Draw the structure of the molecule of cyclohexane (C6H12). OR (b) (i) Name a commercially important carbon compound having functional group -OH and write its molecular formula. (ii) Write chemical equation to show its reaction with (1) Sodium metal (2) Excess conc. sulphuric acid (3) Ethanoic acid in the presence of an acid catalyst (4) Acidified potassium dichromate Also write the name of the product formed in each case.

   

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   Watch it on the board · 125 s

   Model answer · covalent bonding, homologous series

   1. 1.(a) (i) A carbon atom has 4 electrons in its outermost shell. Carbon cannot form C4+ cations because removing 4 electrons from a carbon atom would need a large amount of energy. It cannot form C4- anions because it would be difficult for a nucleus with 6 protons to hold 10 electrons.1 mark
   2. 2.So carbon shares its 4 valence electrons with other atoms. This lets it complete its octet, and it forms covalent bonds, which give covalent compounds.1 mark
   3. 3.(ii) A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in carbon chains of different lengths. All its members have similar chemical properties, and each member differs from the next by a –CH2– unit.1 mark
   4. 4.Two consecutive members of the homologous series of aldehydes are CH3CHO (ethanal) and C2H5CHO (propanal). They differ by one –CH2– unit.1 mark
   5. 5.(iii) Cyclohexane (C6H12) is a ring of six carbon atoms joined to each other by single bonds. Each carbon atom is also joined to two hydrogen atoms by single bonds: H2C — CH2 / \ H2C CH2 \ / H2C — CH21 mark

   Diagram: Draw a hexagonal ring of six carbon atoms joined by single bonds. Each carbon carries two hydrogen atoms (–CH2–). Label it 'Cyclohexane (C6H12)'.

   • For (i), write both reasons: 'a large amount of energy' for C4+, and 'a nucleus with 6 protons to hold 10 electrons' for C4-. Then add that carbon shares electrons to form covalent bonds.
   • In the definition, write 'same functional group' and 'similar chemical properties'.
   • In the cyclohexane structure, show all six carbons in a closed ring, with two hydrogens on each carbon.

   Marks split as in the board’s published marking scheme

2. Q2Long answer5 marksAsked: 2023

   (a) A saturated organic compound ‘A’ belongs to the homologous series of alcohols. On heating ‘A’ with concentrated sulphuric acid at 443 K, it forms an unsaturated compound ‘B’ with molecular mass 28 u. The compound ‘B’ on addition of one mole of hydrogen in the presence of Nickel, changes to a saturated hydrocarbon ‘C’. (i) Identify A, B and C. (ii) Write the chemical equations showing the conversion of A into B. (iii) What happens when compound C undergoes combustion ? (iv) State one industrial application of hydrogenation reaction. (v) Name the products formed when compound A reacts with sodium. OR (b) (i) With the help of diagram, show the formation of micelles, when soap is applied on oily dirt. (ii) Take two test tubes X and Y with 10 mL of hard water in each. In test tube ‘X’, add few drops of soap solution and in test tube ‘Y’ add a few drops of detergent solution. Shake both the test tubes for the same period. (1) In which test tube the formation of foam will be more ? Why ? (2) In which test tube is a curdy solid formed ? Why ?

   

   Medha Ma’am

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   Model answer · ethanol dehydration, ethene, ethane reactions

   1. 1.(a)(i) A is ethanol (C₂H₅OH), B is ethene (C₂H₄, 28 u) and C is ethane (C₂H₆). OR (b)(i) Diagram: soap molecules around the oily dirt, their hydrocarbon tails pointing into the oil at the centre and their ionic heads facing outwards into the water.1.5 marks
   2. 2.(a)(ii) CH₃CH₂OH → (conc. H₂SO₄, 443 K) CH₂=CH₂ + H₂O; the acid acts as a dehydrating agent. OR The oily dirt collects in the centre of the micelle, the micelles stay in the water as an emulsion, and the dirt is washed away.1 mark
   3. 3.(a)(iii) Ethane burns to give carbon dioxide and water, with heat and light. OR (b)(ii)(1) More foam forms in Y, because detergents do not form insoluble precipitates with the calcium and magnesium ions of hard water.1 mark
   4. 4.(a)(iv) Vegetable oils are hydrogenated with a nickel catalyst to make vanaspati ghee. OR (b)(ii)(2) The curdy solid forms in X.0.5 marks
   5. 5.(a)(v) Ethanol and sodium give sodium ethoxide and hydrogen gas. OR Soap reacts with the calcium and magnesium ions of hard water to form an insoluble substance (scum), seen as a curdy solid.1 mark

   Marks split from a structure derived from past papers (checked twice); not CBSE’s official scheme

3. Q3Long answer5 marksAsked: 2026

   (a) (i) Give reasons for the following : (I) Covalent compounds are poor conductor of electricity. (II) Soap does not form lather in hard water. (III) Carbon shows catenation but silicon does not. (ii) Write chemical equations for the following : (I) Oxidation of ethanol by acidified K2Cr2O7. (II) Hydrogenation of ethene. OR (b) Mohan heated ethanol with a compound 'X' in the presence of a few drops of conc. H2SO4 and observed a sweet smelling compound 'Y' is formed. When 'Y' is treated with sodium hydroxide it gives back ethanol and a compound 'Z'. (i) Identify 'X', 'Y' and 'Z'. (ii) Write the role of conc. H2SO4 in the reaction. (iii) Write the chemical equations involved and name the reactions.

   

   Medha Ma’am

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   Model answer · Carbon compounds: reasons and equations

   1. 1.(a) (i) (I) Covalent compounds are poor conductors of electricity because they do not give rise to charged particles or ions. In covalent bonds, electrons are shared between two atoms, not transferred, so no ions are formed that could carry current.1 mark
   2. 2.(II) Soap does not form lather in hard water because soap reacts with the calcium and magnesium salts present in hard water. This reaction forms an insoluble substance called scum. So foam forms with difficulty, and a larger amount of soap is needed.1 mark
   3. 3.(III) Carbon shows catenation but silicon does not because C–C bonds are strong and stable, whereas Si–Si bonds are relatively weak. So carbon can join with other carbon atoms to form long chains, but silicon cannot form stable long chains.1 mark
   4. 4.(ii) (I) Ethanol is oxidised to ethanoic acid by acidified K2Cr2O7 on heating: CH3CH2OH --(acidified K2Cr2O7 + heat)--> CH3COOH (Ethanol) → (Ethanoic acid)1 mark
   5. 5.(II) In hydrogenation, hydrogen is added to ethene in the presence of a nickel catalyst to give ethane: CH2=CH2 + H2 --(Ni)--> CH3–CH3 (Ethene) → (Ethane)1 mark

   • For (I), write that covalent compounds "do not give rise to charged particles or ions".
   • For hard water, name both "calcium and magnesium salts" and the insoluble substance "scum".
   • Write the conditions above the arrow: "acidified K2Cr2O7 + heat" for oxidation and "Ni" for hydrogenation.

   Marks split as in the board’s published marking scheme

4. Q4Case-based5 marksAsked: 2026

   Attempt either (a) or (b) : (a) (i) What is homologous series ? Which two of the following organic compounds belong to the same homologous series ? C2H4, C4H10, C3H4, C4H8 (ii) Write the product(s) in the following reactions : (I) CH3 - CH2 - OH + CH3COOH --Acid--> (II) C2H5OH + O2 --Burning--> (iii) Why does micelle formation take place when soap is added to water ? OR (b) (i) Name the following compounds : (I) CH3 - C(=O) - CH3 (II) H - C(H)(H) - C ≡ C - H (ii) Name the reaction which is commonly used in the conversion of vegetable oils to fats. (iii) Why is the melting point of C4H10 higher than C3H8 ? (iv) What happens when a piece of sodium is dropped into ethanol ? (v) Write the products in the following reaction : CH3COOC2H5 + NaOH ---->

   How the model answer begins

   1. (a) (i) A homologous series is a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain. Its members can be represented by a single general formula, and successive members…

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5. Q5Long answer5 marksAsked: 2026

   Attempt either (a) or (b) : (a) (i) What is homologous series ? Which two of the following organic compounds belong to the same homologous series ? C2H4, C4H10, C3H4, C4H8 (ii) Write the product(s) in the following reactions : (I) CH3 - CH2 - OH + CH3COOH --Acid--> (II) C2H5OH + O2 --Burning--> (iii) Why does micelle formation take place when soap is added to water ? OR (b) (i) Name the following compounds : (I) CH3 - C(=O) - CH3 (II) H - C(H)(H) - C(triple bond)C - H (ii) Name the reaction which is commonly used in the conversion of vegetable oils to fats. (iii) Why is the melting point of C4H10 higher than C3H8 ? (iv) What happens when a piece of sodium is dropped into ethanol ? (v) Write the products in the following reaction : CH3COOC2H5 + NaOH ---->

   How the model answer begins

   1. (a) (i) A homologous series is a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain. Its members can be represented by a single general formula, and successive members…

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6. Q6Short answer5 marksAsked: 2026

   29. Attempt either option (A) or (B) : (A) (i) Carbon cannot form C4+ cation and C4- anion. Explain. (ii) Define homologous series of carbon compounds. Why are the melting and boiling points of C4H10 higher than C3H8 or C2H6 ? (iii) What happens when ethanol is heated with acidified potassium dichromate ? OR (B) (i) How would you name the following : I. CH3 - CH2 - C = O | H II. CH3 - C = CH (ii) When ethanol reacts with ethanoic acid in the presence of conc. H2SO4, 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. (iii) Why soaps do not produce foam with hard water ?

   How the model answer begins

   1. (i) Carbon has four electrons in its outermost shell. It cannot form the C4+ cation because the removal of four electrons needs a very large amount of energy, so it is energetically not possible. It cannot form the C4-…

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7. Q7Long answer5 marksAsked: 2025

   (A) A carbon compound 'A' on heating with excess conc. H2SO4 forms another compound 'B' which on addition of 1 mole of hydrogen gas in the presence of nickel catalyst forms a compound 'C'. Compound 'C' on combustion forms two moles of carbon dioxide and three moles of water. Identify 'A', 'B' and 'C' and write their structures. Give the equations of the reactions that take place. Also mention the role of conc. sulphuric acid in the formation of 'B' from 'A'. OR (B) A carbon compound 'A' is used as a preservative for pickles and has a molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound 'B'. (i) Identify compound 'A' and write its structure. (ii) Write the chemical equation for the reaction of compound 'A' with ethanol in which 'B' is formed. Mention the role of the presence of an acid in this reaction. (iii) How can we get back compound 'A' from compound 'B'? (iv) How can 'A' be obtained from ethanol? (v) Name the gas evolved in the reaction of compound 'A' with washing soda.

   How the model answer begins

   1. (A) Compound 'A' is ethanol (ethyl alcohol), CH3CH2OH. Its structure is CH3–CH2–OH: two carbon atoms joined by a single bond, with an –OH group on one carbon. Heating it with excess concentrated sulphuric acid gives an…

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8. Q8Long answer5 marksAsked: 2025

   (A) (i) What are structural isomers? Draw the structural isomers of butane (C4H10). Give reason why propene does not have any structural isomer. (ii) What happens when butane is burnt in air? Write the chemical equation of the reaction that takes place. Distinguish between the flames obtained on burning butane and butyne when both are burnt in air under similar conditions. OR (B) (i) Give reason why carbon can neither form C4+ cation nor C4- anion, but forms covalent compounds. (ii) What is meant by functional group of carbon-compounds? Write the structural formula and the functional group present in the following compounds in a tabular form: (a) Ethanol (b) Ethanoic acid

   How the model answer begins

   1. (A)(i) Structural isomers are compounds with the same molecular formula but different structures. OR (B)(i) Carbon cannot form C⁴⁺, because removing four electrons needs a very large amount of energy.

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9. Q9Long answer5 marksAsked: 2025

   (a) Name an alcohol and a carboxylic acid having two carbon atoms in their structures. Draw their structures and state how this alcohol can be converted into a carboxylic acid. What happens when these two compounds react in the presence of an acid ? Write chemical equations for the reactions involved in the two cases mentioned above. OR (b) What are soaps ? Write the structure of a soap molecule. Explain the cleansing action of a soap. Why are soaps not considered suitable for washing clothes in a region where water is hard ? How is this problem overcome ?

10. Q10Long answer5 marksAsked: 2024

    (A) (i) Define a homologous series of carbon compounds. (ii) Why is the melting and boiling points of C4H8 higher than that of C3H6 or C2H4 ? (iii) Why do we NOT see any gradation in chemical properties of a homologous series compounds ? (iv) Write the name and structures of (i) aldehyde and (ii) ketone with molecular form C3H6O. OR (B) (i) Write the name and structure of an organic compound 'X' having two carbon atoms in its molecule and its name is suffixed with '-ol'. (ii) What happens when 'X' is heated with excess concentrated sulphuric acid at 443 K? Write chemical equation for the reaction stating the conditions for the reaction. Also state the role played by concentrated sulphuric acid in the reaction. (iii) Name and draw the electron dot structure of hydrocarbon produced in the above reaction.

    How the model answer begins

    1. (A) (i) A homologous series is a series of carbon compounds in which the same functional group substitutes for hydrogen in a carbon chain. This means the same functional group is attached to carbon chains of different…

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11. Q11Long answer5 marksAsked: 2023

    (A) (i) Draw the structure of the following compounds : (a) Butanoic acid (b) Chloropentane (ii) How are structure (i) and structure (ii) given below related to one another ? Give reason to justify your answer. [Structure (i) and (ii) diagrams] Draw one more possible structure for above case. (iii) Differentiate between saturated and unsaturated carbon compounds on the basis of their general formula. OR (B) (i) What happens when a small piece of sodium is dropped in ethanol ? Write the equation for this reaction. (ii) Why is glacial acetic acid called so ? (iii) What happens when ethanol is heated at 443 K in the presence of conc. H2SO4 ? Write the role of conc. H2SO4 in this case. (iv) Write an equation showing saponification.

12. Q12Long answer5 marksAsked: 2026

    (a) Attempt either (k) or (kh) : (k) C_2H_6O molecular formula carbon compound 'P' was found neutral on testing with red and blue litmus. When sodium metal reacts with compound 'P' then a gas is produced which burns with a pop sound. (i) Identify the compound 'P'. (ii) To produce compound 'Q', carbon compound 'P' is heated with conc. H_2SO_4 at 443 K. (I) Write the chemical equation for the reaction. (II) What is the role of conc. H_2SO_4 in this reaction ? (iii) What will be the expected observation on heating compound 'P' with ethanoic acid in the presence of an acid as a catalyst ? Write the chemical equation for the reaction. OR (kh) (i) Write the structural formula of benzene. (ii) Give reasons why carbon neither forms C^4+ cation nor C^4- anion. (iii) What type of bond is formed between carbon and hydrogen ? (iv) How is ethanol converted into ethanoic acid ? (v) Complete the following chemical equation : CH_3COOC_2H_5 + NaOH ->

    How the model answer begins

    1. (k)(i) P is ethanol (C₂H₅OH): it is neutral to litmus and gives hydrogen (pop sound) with sodium. OR (kh)(i) Benzene, C₆H₆: a hexagonal ring of six carbon atoms with alternate single and double bonds and one hydrogen on…

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13. Q13Long answer5 marksAsked: 2026

    Attempt either (a) or (b) : (a) A carbon compound 'P' of molecular formula C2H6O is found to be neutral when tested with red and blue litmus. A gas that burns with a pop sound is produced when sodium metal reacts with compound 'P'. (i) Identify the compound 'P'. (ii) The carbon compound 'P' is heated with conc. H2SO4 at 443 K to produce compound 'Q'. (I) Write the chemical equation for the reaction. (II) What is the role of conc. H2SO4 in this reaction ? (iii) What is likely to be observed on heating compound 'P' with ethanoic acid with an acid as a catalyst ? Write the chemical equation for the reaction. OR (b) (i) Write the structural formula of benzene. (ii) State the reason why carbon can neither form C4+ cation nor C4- anion. (iii) What type of bond is formed between carbon and hydrogen ? (iv) How is ethanol converted to ethanoic acid ? (v) Complete the following chemical equation : CH3COOC2H5 + NaOH ---->

    How the model answer begins

    1. (a)(i) P is ethanol (C₂H₅OH): it is neutral to litmus and gives hydrogen (pop sound) with sodium. OR (b)(i) Benzene, C₆H₆: a hexagonal ring of six carbon atoms with alternate single and double bonds and one hydrogen on…

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14. Q14Long answer5 marksAsked: 2025

    (a) (i) Draw two isomeric structures of Butene (C4H8). (ii) Name the following compounds : (I) H-C-C-C-Cl (with H atoms) (II) H-C-C-C-C-H (with H and O atoms) (iii) Write the chemical equations for the following reactions. Mention one essential condition each for these reactions to take place. (I) Ethanol undergoes complete oxidation (II) Propene undergoes hydrogenation (III) Ethanoic acid reacts with ethanol OR (b) (i) A carbon compound X is a good solvent. On reaction with sodium, X forms two products Y and Z. Z is used to convert vegetable oil into vegetable ghee. Identify and name X, Y and Z. Also write the equation of reaction of X with sodium to justify your answer. (ii) Write chemical equation to show what happens when ethanol : (I) burns in oxygen/air. (II) is heated at 443 K in excess conc. H2SO4. (III) reacts with acidified potassium dichromate.

    How the model answer begins

    1. (a)(i) But-1-ene CH₂=CH–CH₂–CH₃ and but-2-ene CH₃–CH=CH–CH₃. OR (b)(i) X is ethanol (C₂H₅OH) and Y is sodium ethoxide (C₂H₅ONa).

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15. Q15Long answer5 marksAsked: 2025

    (a) A saturated organic compound 'A' with two carbon atoms belongs to the homologous series of alcohols. On oxidation, it forms an organic acid 'B' with molecular mass 60 u. On heating 'A' with excess concentrated sulphuric acid at 443 K, an unsaturated hydrocarbon 'C' is formed. (i) Name A, B and C. (ii) Calculate molecular mass of C. (iii) What happens when a pinch of sodium carbonate is added to compound B ? Write chemical equation for the reaction. (iv) Draw electron dot structure of compound B. OR (b) (i) What is a homologous series of carbon compounds ? Write the name and formula of three successive members of the homologous series of compounds having functional group - COOH. (ii) Write the name of two carbon compounds in which carbon atoms are arranged in the form of a ring. Draw the structure of any one of the two.

    How the model answer begins

    1. (a)(i) A is ethanol (C₂H₅OH), B is ethanoic acid (CH₃COOH) and C is ethene (C₂H₄). OR (b)(i) A homologous series is a series of carbon compounds with the same functional group and similar chemical properties, in which…

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16. Q16Long answer5 marksAsked: 2025

    (a) (i) Draw electron dot structure of chlorine molecule. (Atomic Number of Chlorine = 17) (ii) What happens when chlorine reacts with methane in the presence of sunlight ? Write the name of the reaction. (iii) [continues on next page]

17. Q17Long answer5 marksAsked: 2025

    (a) (i) A compound 'X' having two carbon atoms in its molecule turns blue litmus red and 5 – 8% solution of 'X' in water is widely used as a preservative. Identify the compound 'X' and write its structure. (ii) Compare its pH nature with a mineral acid. (iii) 'X' on reacting with alcohols produces sweet smelling compounds, used in making perfumes. Name the reaction and write its chemical equation. (iv) When sodium carbonate is added to 'X', a colourless gas is produced which turns lime water milky. Write the chemical equation for the reaction giving the name of the salt produced. OR (b) (i) Differentiate between saturated and unsaturated hydrocarbons by giving one example each, with a structural formula. (ii) Write the method of converting an unsaturated hydrocarbon into a saturated hydrocarbon. Name the industry where this reaction is commonly used. (iii) Write the name and structure of a hydrocarbon having double bond and four carbon atoms in its one molecule.

    How the model answer begins

    1. (a) (i) The compound 'X' is ethanoic acid, which is commonly called acetic acid. It belongs to the group of carboxylic acids, so it turns blue litmus red. A 5-8% solution of acetic acid in water is called vinegar and is…

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18. Q18Long answer5 marksAsked: 2025

    34. (a) (i) A compound 'X' having two carbon atoms in its molecule turns blue litmus red and 5 - 8% solution of 'X' in water is widely used as a preservative. Identify the compound 'X' and write its structure. (ii) Compare its pH nature with a mineral acid. (iii) 'X' on reacting with alcohols produces sweet smelling compounds, used in making perfumes. Name the reaction and write its chemical equation. (iv) When sodium carbonate is added to 'X', a colourless gas is produced which turns lime water milky. Write the chemical equation for the reaction giving the name of the salt produced. OR (b) (i) Differentiate between saturated and unsaturated hydrocarbons by giving one example each, with a structural formula. (ii) Write the method of converting an unsaturated hydrocarbon into a saturated hydrocarbon. Name the industry where this reaction is commonly used. (iii) Write the name and structure of a hydrocarbon having double bond and four carbon atoms in its one molecule.

    How the model answer begins

    1. (a) (i) The compound 'X' is ethanoic acid, commonly called acetic acid. It has two carbon atoms, it is a carboxylic acid, so it turns blue litmus red, and its 5-8% solution in water is called vinegar, which is used…

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19. Q19Long answer5 marksAsked: 2025

    (A) (a) What is meant by the term homologous series of carbon compounds ? Write molecular formula of any two consecutive members of homologous series of ketones. (b) Write chemical equation of the reactions of ethanoic acid with (i) Sodium hydroxide and (ii) Ethanol (in the presence of an acid); giving the name of the products in each case. (c) Draw the structure of the molecule of benzene. OR (B) (a) Write the molecular formula of ethene and draw its electron-dot structure. (b) Write chemical equations of the reactions of ethanol with (i) Sodium metal (ii) Ethanoic acid (in the presence of an acid) and (iii) Acidified potassium dichromate. Also mention the name of the products formed in each case.

    How the model answer begins

    1. (a) A homologous series is a series of carbon compounds in which the same functional group is attached to carbon chains of different lengths. Its members have the same general formula and similar chemical properties,…

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20. Q20Long answer5 marksAsked: 2025

    35. (A) (a) Define the term "homologous series of carbon compounds". Write a homologous series of compounds having functional group - CHO. (b) Design an experiment to distinguish between an alcohol and a carboxylic acid. Also write chemical equation for that case in which reaction occurs. OR (B) (a) Define the term "structural isomers". Write the structures of two isomers of butane (C4H10). (b) Two carbon compounds X and Y have the molecular formula C2H4 and C3H8 respectively. Which one of the two is most likely to show addition reaction ? Justify your answer. Also give (i) chemical equation to explain the process of addition reaction in this case and (ii) name of the industry where this reaction is applied.

    How the model answer begins

    1. (A)(a) A homologous series is a series of carbon compounds with the same functional group and similar chemical properties, successive members differing by a –CH₂– unit. OR (B)(a) Structural isomers are compounds with…

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Objective questions with the board’s key (10)

1. 1. CBSE 2026

   Directions : For question number 24, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to this question from the codes (A), (B), (C) and (D) as given below : Assertion (A) : Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements. Reason (R) : The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.

   • (A) Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). ✓
   • (B) Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (A)

2. 2. CBSE 2026

   20. Which of the following functional groups is that of carboxylic acid ?

   • (A) -OH
   • (B) -C=O-OH ✓
   • (C) -C=O-
   • (D) -C=O-H

   Answer: (B)

3. 3. CBSE 2026

   Consider the structures 'X' and 'Y' given below : Which of the following statements are correct ? (i) 'X' and 'Y' are homologues. (ii) 'X' and 'Y' have the same structural formula, but different molecular formula. (iii) 'X' and 'Y' have the same molecular formula, but different structural formula. (iv) 'X' and 'Y' are structural isomers.

   • (A) (i) and (iii)
   • (B) (i) and (iv)
   • (C) (ii) and (iv)
   • (D) (iii) and (iv) ✓

   Answer: (D)

4. 4. CBSE 2026

   Which of the following compounds will undergo addition reaction ?

   • (A) C4H10
   • (B) C4H8 ✓
   • (C) C3H8
   • (D) CH4

   Answer: (B)

5. 5. CBSE 2026

   Assertion (A) : Carbon compounds are in large number, in which many carbon atoms are linked to each other. Reason (R) : Carbon-carbon bond is very strong and stable.

   • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A). ✓
   • (B) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
   • (C) Assertion (A) is true but Reason (R) is false.
   • (D) Assertion (A) is false but Reason (R) is true.

   Answer: (A)

6. 6. CBSE 2026

   While washing dirty clothes by soap, micelles are formed. Select the correct statement about micelles.

   • (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. ✓
   • (B) The hydrophobic tail is on the surface of the cluster, whereas hydrophilic end is in the interior of cluster.
   • (C) Both hydrophobic tail and hydrophilic end are in the interior of the cluster.
   • (D) Both hydrophobic tail and hydrophilic end are on the surface of the cluster.

   Answer: (A)

7. 7. CBSE 2026

   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.

   • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). ✓
   • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (A)

8. 8. CBSE 2026

   The formula of functional group for aldehyde is :

   • (A) -COOH
   • (B) -CHO ✓
   • (C) -C=O
   • (D) -OH

   Answer: (B)

9. 9. CBSE 2026

   Assertion (A) : Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements. Reason (R) : The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.

   • (A) Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). ✓
   • (B) Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
   • (C) Assertion (A) is true, but Reason (R) is false.
   • (D) Assertion (A) is false, but Reason (R) is true.

   Answer: (A)

10. 10. CBSE 2026

    Assertion (A) : Carbon compounds can form straight, branched and ring structures. Reason (R) : Carbon exhibits the property of catenation.

    • (A) Assertion (A) and Reason (R) both are correct and Reason (R) is the correct explanation of Assertion (A). ✓
    • (B) Assertion (A) and Reason (R) both are correct, but Reason (R) is not the correct explanation of Assertion (A).
    • (C) Assertion (A) is correct, but Reason (R) is incorrect.
    • (D) Assertion (A) is incorrect, but Reason (R) is correct.

    Answer: (A)

Questions parents and students ask

How many marks does "Carbon and its Compounds" carry in CBSE Class 10 Science?

In the CBSE papers of 2023–2026, this chapter carried about 6 marks and about 2 questions a year; by marks it ranks 6 in Science.

Which are the most important (VVI) questions of "Carbon and its Compounds"?

The 20 questions above are from the board’s real papers, each with the years it was asked; the most-asked come first with their full model answers. All 35 written questions of this chapter, with answers, are in the Ask Medha app.

Do the answers follow the board’s marking scheme?

Yes. CBSE publishes its marking schemes; every model answer here is written point by point to the marks the board’s own scheme gives, and checked by a second, independent model.