CBSE Important Questions Class 10 Science Chapter 4 Carbon and Its Compounds

CBSE important questions class 10 science chapter 4 are exam-focused questions from Carbon and Its Compounds, Chapter 4 of NCERT Class 10 Science (Reprint 2026-27). The chapter covers catenation, tetravalency, covalent bonding, homologous series, functional groups, chemical reactions of carbon compounds, ethanol, ethanoic acid, and soaps and detergents — all mapped to the 2026 CBSE board exam pattern.

Carbon and Its Compounds is one of the most scoring chapters in Class 10 Science. It produces predictable questions across every mark category in board exams. Students who revise catenation, esterification, saponification, and the soap cleaning mechanism systematically rarely lose marks here. This page gives you the complete set of carbon and its compounds class 10 important questions with answers, covering MCQs, 2-mark, 3-mark, and 5-mark questions, plus PYQ-style and extra questions. Save this alongside your chapter notes or carbon and its compounds class 10 pdf for targeted pre-board revision.

Key Takeaways

CBSE Class 10 Science All Chapters at a Glance

Class 10 Carbon and Its Compounds: What to Focus On

Carbon and its compounds is a chapter where board questions repeat in recognisable patterns every year. Catenation and tetravalency form the conceptual base. Reactions — esterification, saponification, oxidation, addition, and substitution — generate the most 3-mark and 5-mark questions. The soap cleaning mechanism and the difference between soap and detergent appear consistently as long-answer questions. Students searching for class 10 carbon and its compounds question answer sets should prioritise these areas before moving to nomenclature and structural isomers.

Very Short Answer Questions — Carbon and Its Compounds Class 10 (1 Mark)

These MCQs and one-line answers are directly from the NCERT exercise and common board patterns. Carbon and its compounds class 10 questions at 1-mark level test recall of definitions, functional groups, and reaction types.

Q1. Ethane (C₂H₆) has how many covalent bonds? (a) 6 (b) 7 (c) 8 (d) 9 Ans: (b) 7. One C–C bond and six C–H bonds. Total = 7 covalent bonds.

Q2. Butanone is a four-carbon compound with the functional group: (a) Carboxylic acid (b) Aldehyde (c) Ketone (d) Alcohol Ans: (c) Ketone. The suffix –one indicates a ketone functional group.

Q3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means: (a) Food is not cooked completely (b) Fuel is not burning completely (c) Fuel is wet (d) Fuel is burning completely Ans: (b) Fuel is not burning completely. Incomplete combustion produces carbon soot, which blackens the vessel.

Q4. The functional group present in butanol is: (a) Ketone (b) Aldehyde (c) Hydroxyl (–OH) (d) Carboxyl Ans: (c) Hydroxyl (–OH). The suffix –ol indicates an alcohol.

Q5. Out of butter and groundnut oil, which is unsaturated? Ans: Groundnut oil. It contains long chains with double bonds (unsaturated fatty acids). Butter contains saturated fatty acids.

Q6. Which substance is added to make ethanol unfit for drinking? Ans: Methanol. Methanol is poisonous and is added to produce denatured alcohol.

Q7. Which ions are responsible for making water hard? Ans: Ca²⁺ and Mg²⁺ ions. Bicarbonates, chlorides, and sulphates of calcium and magnesium cause hardness.

Q8. Buckminsterfullerene is an allotropic form of: (a) Phosphorus (b) Sulphur (c) Carbon (d) Tin Ans: (c) Carbon. C₆₀ has carbon atoms arranged in a football shape.

Q9. The IUPAC name of the first member of the ketone homologous series is: (a) Ethanone (b) Methanone (c) Propanone (d) Butanone Ans: (c) Propanone. CH₃COCH₃ has a 3-carbon parent chain.

Q10. Which of the following undergo addition reactions? C₂H₆, C₃H₈, C₃H₆, C₂H₂, CH₄ Ans: C₃H₆ (propene) and C₂H₂ (ethyne). Only unsaturated compounds undergo addition reactions.

Q11. The odour of ethanoic acid resembles: (a) Rose (b) Burning plastic (c) Vinegar (d) Kerosene Ans: (c) Vinegar. Vinegar is a 5–8% solution of acetic acid in water.

Q12. Carbon exists in the atmosphere mainly as: (a) Carbon monoxide (b) Both CO and CO₂ (c) Carbon dioxide (d) Coal Ans: (c) Carbon dioxide. The atmosphere contains approximately 0.03% CO₂.

Carbon and Its Compounds Class 10 Questions with Answers (2 Marks)

These are the most frequently tested carbon and its compounds class 10 questions with answers at the 2-mark level. Board exams typically ask 2-3 questions from this category covering properties, reactions, and distinctions.

Q13. What are the two properties of carbon that lead to the huge number of carbon compounds? Ans: Catenation is the ability of carbon to form strong covalent bonds with other carbon atoms, creating long chains, branched chains, and rings. The C–C bond is very stable. Tetravalency means carbon has a valency of four. It can bond with four atoms of carbon or other elements like hydrogen, oxygen, nitrogen, sulphur, and chlorine, producing enormous structural variety.

Q14. What is a homologous series? Give one example. Ans: A homologous series is a group of carbon compounds sharing the same functional group and similar chemical properties. Each successive member differs by a –CH₂– unit (molecular mass difference of 14 u). Example: Alkanes — CH₄, C₂H₆, C₃H₈, C₄H₁₀, following the general formula CₙH₂ₙ₊₂.

Q15. Why is the conversion of ethanol to ethanoic acid an oxidation reaction? Ans: Ethanoic acid has one more oxygen atom and two fewer hydrogen atoms than ethanol. Gain of oxygen and loss of hydrogen are both signs of oxidation. Both happen in this conversion, so it is an oxidation reaction. Reaction: CH₃CH₂OH → (alkaline KMnO₄ + heat) → CH₃COOH.

Q16. A mixture of oxygen and ethyne is used for welding. Why is ethyne and air not used? Ans: Ethyne burning in pure oxygen produces a flame of about 3300 K through complete combustion. In air, nitrogen dilutes the oxygen and causes incomplete combustion, producing a sooty, cooler flame. This temperature is insufficient for welding metals, so pure oxygen is used instead of air.

Q17. Would you be able to check if water is hard using a detergent? Ans: No. Detergents are sulphonic acid salts. Their charged ends do not form insoluble precipitates with Ca²⁺ and Mg²⁺ ions in hard water. Detergents lather equally well in both hard and soft water, so they cannot detect water hardness.

Q18. How would you distinguish experimentally between an alcohol and a carboxylic acid? Ans: Add sodium hydrogen carbonate (NaHCO₃) to each. Carboxylic acid reacts with NaHCO₃ to produce CO₂, which turns lime water milky: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂. Alcohol shows no reaction with NaHCO₃ and produces no gas.

Q19. Why are carbon compounds used as fuels for most applications? Ans: Carbon compounds have high calorific values and burn in oxygen to release large amounts of heat and light. Saturated hydrocarbons like methane burn cleanly, producing only CO₂ and water. These highly exothermic reactions make carbon compounds ideal fuels for domestic, transport, and industrial use.

Q20. Why is agitation necessary when washing with soap? Ans: Soap forms micelles around oily dirt where the hydrophobic tails trap oil and hydrophilic heads face water. Agitation — scrubbing or machine washing — dislodges these micelles from cloth fibres and disperses them into the wash water. Rinsing then removes the dirt-filled micelles completely.

Important Questions from Carbon and Its Compounds (3 Marks)

Important questions from carbon and its compounds at the 3-mark level require structured answers covering comparison, reaction writing, and structural diagrams. These are among the highest-value questions in the carbon and its compounds important questions set for 2026 board exams.

Ethanol vs Ethanoic Acid

Q21. How can ethanol and ethanoic acid be differentiated on the basis of physical and chemical properties? Ans:

Physical properties: Ethanol is a liquid with a pleasant smell and melting point 156 K. Ethanoic acid smells like vinegar with a melting point of 290 K. It freezes in cold climates and is called glacial acetic acid.

Chemical properties — NaHCO₃ test: Ethanoic acid produces CO₂: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂. Ethanol shows no reaction.

Litmus test: Ethanoic acid turns blue litmus red. Ethanol has no effect on litmus.

Esterification

Q22. What is esterification? Write the reaction and state the role of concentrated H₂SO₄. Ans: Esterification is the reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst to form an ester and water.

CH₃COOH + CH₃CH₂OH ⇌ (conc. H₂SO₄) → CH₃COOC₂H₅ + H₂O

Esters are sweet-smelling compounds used in perfumes and flavouring agents. Conc. H₂SO₄ acts as a catalyst and dehydrating agent. It removes water from the mixture, shifting equilibrium forward and increasing ester yield.

Bromine Water Test

Q23. Give a chemical test to distinguish between saturated and unsaturated hydrocarbons. Ans: The bromine water test is the standard method. Add a few drops of reddish-brown bromine water to each compound. An unsaturated hydrocarbon (alkene or alkyne) decolourises the bromine water because bromine adds across the double or triple bond. A saturated hydrocarbon (alkane) leaves the bromine water colour unchanged because no addition reaction occurs.

Structural Drawing

Q24. Draw the structures for: (i) Ethanoic acid (ii) Butanone (iii) Hexanal Ans:

(i) Ethanoic acid (CH₃COOH): H₃C–C(=O)–OH

(ii) Butanone (CH₃COCH₂CH₃): 4-carbon chain with C=O at carbon 2.

(iii) Hexanal (CH₃CH₂CH₂CH₂CH₂CHO): 6-carbon chain with –CHO at carbon 1.

Saponification

Q25. What is saponification? Write the reaction involved. Ans: Saponification is the hydrolysis of an ester by an alkali to produce an alcohol and the salt of a carboxylic acid. This salt is soap.

CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH

Soaps are sodium or potassium salts of long-chain fatty acids. Saponification is the chemical basis of soap manufacture.

Functional Group Identification

Q26. Name the functional groups present in the following: (a) CH₃COCH₂CH₂CH₂CH₃ (b) CH₃CH₂CH₂COOH (c) CH₃CH₂CH₂CH₂CHO (d) CH₃CH₂OH

Ans: (a) Ketone (>C=O) — carbonyl group in the middle of the chain (b) Carboxylic acid (–COOH) (c) Aldehyde (–CHO) — carbonyl group at terminal carbon (d) Alcohol (–OH)

Carbon and Its Compounds Class 10 Important Questions (5 Marks)

Five-mark questions from carbon and its compounds class 10 extra questions with answers test the ability to write structured, detailed answers. The soap mechanism and compound identification questions are the most repeated 5-mark patterns in board exams.

Q27. Explain the mechanism of the cleaning action of soaps. Why does soap not work well in hard water?

Soap molecules are sodium or potassium salts of long-chain carboxylic acids with two distinct ends. The hydrophilic ionic head interacts with water. The hydrophobic carbon-chain tail interacts with oil and grease.

When soap is added to dirty water, the hydrophobic tails orient towards oily dirt and the hydrophilic heads face outward towards water. This creates micelles — spherical clusters where dirt is trapped inside. Ion-ion repulsion between the ionic heads keeps the micelles suspended as a stable colloid. Agitation dislodges these micelles from cloth fibres. Rinsing carries the dirt-filled micelles away.

Hard water contains Ca²⁺ and Mg²⁺ ions. These react with soap molecules to form insoluble calcium and magnesium salts of fatty acids — this insoluble precipitate is called scum. Scum sticks to the container and clothes without cleaning them. Large amounts of soap get wasted in forming scum before any actual cleaning begins. Detergents overcome this because their charged ends do not form precipitates with Ca²⁺ and Mg²⁺ ions.

Q28. An organic compound A is used as a preservative in pickles with molecular formula C₂H₄O₂. It reacts with ethanol in the presence of an acid to form sweet-smelling compound B. Answer the following: (i) Identify compound A. (ii) Write the equation for its reaction with ethanol. (iii) How can compound A be obtained back from B? (iv) Name the process and write the equation. (v) Which gas is produced when compound A reacts with washing soda?

Ans: (i) Compound A is ethanoic acid (CH₃COOH). It is used as vinegar in pickles.

(ii) Esterification — reaction with ethanol to form ethyl ethanoate (B): CH₃COOH + CH₃CH₂OH ⇌ (conc. H₂SO₄) → CH₃COOC₂H₅ + H₂O

(iii) Treat ester B with NaOH, then acidify the sodium ethanoate formed to regenerate ethanoic acid.

(iv) Saponification: CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH

(v) CO₂ gas is produced when ethanoic acid reacts with washing soda (Na₂CO₃): 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Q29. (a) Why does carbon form the largest number of compounds? (b) Why are some called saturated and others unsaturated? (c) Which is more reactive? (d) Name: (i) CH₃–CH₂–Br (ii) Hex-1-yne

Ans: (a) Carbon forms the largest number of compounds due to catenation (strong C–C bonds creating chains, branches, rings of varying lengths) and tetravalency (four bonds with H, O, N, S, Cl in diverse combinations).

(b) Saturated compounds have only single bonds between carbon atoms and contain maximum hydrogen. Unsaturated compounds have at least one double or triple C–C bond and contain fewer hydrogen atoms.

(c) Unsaturated compounds are more reactive. Double and triple bonds are sites of reactivity and undergo addition reactions readily. Saturated hydrocarbons are fairly inert under normal conditions.

(d) (i) CH₃–CH₂–Br: 2-carbon parent chain with bromine at C1. Name: Bromoethane. (ii) Hex-1-yne: 6-carbon chain with a triple bond at C1. Structure: HC≡C–CH₂–CH₂–CH₂–CH₃

Carbon and Its Compounds Class 10 Extra Questions with Answers

Carbon and its compounds class 10 extra questions cover concepts that appear in board papers beyond direct NCERT exercises. These are particularly useful for students aiming for full marks in the 2026 exam.

Q30. Explain the nature of the covalent bond using bond formation in CH₃Cl. Ans: Carbon needs 4 more electrons to complete its octet but cannot gain or lose 4 electrons easily. Instead, it shares electrons through covalent bonds. In CH₃Cl, carbon shares one electron each with 3 hydrogen atoms (3 C–H bonds) and one electron with chlorine (1 C–Cl bond). Each hydrogen attains helium configuration. Chlorine attains argon configuration. Carbon attains neon configuration. No ions form, which is why CH₃Cl is a poor conductor of electricity.

Q31. Why does micelle formation occur in water but not in ethanol? Ans: In water, soap's hydrophobic tails avoid water and orient inward while hydrophilic heads face outward, forming micelles. In ethanol, the hydrocarbon chain of soap is soluble. There is no separation between hydrophobic and hydrophilic regions. No orientation is needed and micelle formation does not occur.

Q32. Draw the structural isomers of pentane (C₅H₁₂). Ans: Pentane has 3 structural isomers.

n-Pentane: CH₃–CH₂–CH₂–CH₂–CH₃ (straight chain)

Isopentane: CH₃–CH(CH₃)–CH₂–CH₃ (one branch at C2)

Neopentane: C(CH₃)₄ (central carbon with four methyl groups)

All three share the molecular formula C₅H₁₂ but have different arrangements.

Q33. What is hydrogenation? What is its industrial application? Ans: Hydrogenation is the addition of hydrogen to an unsaturated compound using a nickel or palladium catalyst to produce a saturated compound. R–CH=CH–R + H₂ → (Ni) → R–CH₂–CH₂–R. Industrially, hydrogenation converts unsaturated vegetable oils into solid vanaspati ghee. Nickel acts as the catalyst in this process.

Carbon and Its Compounds Class 10 PYQ and Board-Style Questions

Carbon and its compounds class 10 pyq questions from the NCERT exercise and previous board papers follow recognisable patterns. Compound identification questions — where X reacts to give Y and Z — are a consistent PYQ format.

Q34. Compound X (C₂H₆O) is oxidised by alkaline KMnO₄ to give Y. X heated with conc. H₂SO₄ at 443 K gives Z. Z decolourises bromine water. Identify X, Y, and Z. Ans: X = Ethanol (CH₃CH₂OH) — 2-carbon alcohol with formula C₂H₆O. Y = Ethanoic acid (CH₃COOH) — formed by oxidation: CH₃CH₂OH → (alkaline KMnO₄) → CH₃COOH. Z = Ethene (CH₂=CH₂) — formed by dehydration: CH₃CH₂OH → (conc. H₂SO₄, 443 K) → CH₂=CH₂ + H₂O. Ethene is unsaturated and decolourises bromine water.

Q35. Explain the formation of scum when hard water is treated with soap. Ans: Hard water contains dissolved Ca²⁺ and Mg²⁺ salts. These ions react with soap (sodium salt of a fatty acid) to form insoluble calcium and magnesium salts of the fatty acid. For example: 2C₁₇H₃₅COONa + CaCl₂ → (C₁₇H₃₅COO)₂Ca↓ + 2NaCl. The insoluble white precipitate is scum. It sticks to containers and clothes, wastes soap, and prevents cleaning until all Ca²⁺ and Mg²⁺ ions are consumed.

Q36. What change will you observe if you test soap with litmus paper? Ans: Soap is the salt of a weak acid (fatty acid) and a strong base (NaOH). Its aqueous solution is slightly alkaline. Red litmus paper turns blue — confirming alkaline nature. Blue litmus paper remains blue — no change as the solution is already alkaline.