ICSE Class 10 Chemistry: Organic Chemistry — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: What are organic compounds? What is the unique property of carbon that allows it to form so many compounds?
  Ans: Organic compounds are compounds of carbon (except CO, CO₂, carbonates, bicarbonates, and cyanides). Carbon forms millions of compounds due to: (1) Catenation — ability to form bonds with other carbon atoms, creating chains and rings. (2) Tetravalency — carbon has 4 valence electrons, can form 4 covalent bonds. (3) Small atomic size — forms strong, stable bonds.
• Q: What are hydrocarbons? Classify them with examples.
  Ans: Hydrocarbons are organic compounds containing only carbon and hydrogen. Classification: (1) Saturated (Alkanes) — only single bonds, CₙH₂ₙ₊₂. Example: CH₄ (methane), C₂H₆ (ethane). (2) Unsaturated — Alkenes have double bonds (CₙH₂ₙ, example: C₂H₄ ethene) and Alkynes have triple bonds (CₙH₂ₙ₋₂, example: C₂H₂ ethyne).
• Q: Define: (i) Homologous series, (ii) Isomerism. Give examples.
  Ans: (i) Homologous series: A series of organic compounds with same general formula, same functional group, similar chemical properties, and successive members differing by -CH₂- (14 amu). Example: Alkanes — CH₄, C₂H₆, C₃H₈. (ii) Isomerism: Compounds with same molecular formula but different structural arrangements. Example: C₄H₁₀ has two isomers — butane and isobutane.

Long Answer / Application Questions (4-6 Marks)

• Q: What is a functional group? Name the functional groups in (i) alcohol, (ii) aldehyde, (iii) carboxylic acid.
  Ans: A functional group is an atom or group of atoms that determines the chemical properties of an organic compound. (i) Alcohol: -OH (hydroxyl group). Example: CH₃OH (methanol). (ii) Aldehyde: -CHO (aldehyde group). Example: HCHO (methanal/formaldehyde). (iii) Carboxylic acid: -COOH (carboxyl group). Example: CH₃COOH (ethanoic acid/acetic acid).
• Q: Write the IUPAC names: (i) CH₃OH, (ii) CH₃CHO, (iii) CH₃COOH, (iv) CH₃CH₂CH₃.
  Ans: (i) CH₃OH — Methanol (1 carbon + ol suffix for alcohol). (ii) CH₃CHO — Ethanal (2 carbons + al suffix for aldehyde). (iii) CH₃COOH — Ethanoic acid (2 carbons + oic acid for carboxylic acid). (iv) CH₃CH₂CH₃ — Propane (3 carbons + ane suffix for alkane).

Exam Tips for This Chapter

• Revise all definitions and laws from Organic Chemistry — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Organic Chemistry — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Organic Chemistry carries 8-12 marks in the board exam