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Answer the following. (Science 2025 31/1/1 Q34a)

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ScienceCBSE Class 10 · Board exam 2025, set 31/1/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 34(a)

Set in the CBSE Class 10 board exam of 2025, paper 31/1/1, section D, question 34(a), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(a) · 5 marks · Long answerCarbon and its Compounds

Answer the following.

  1. (i)

    Draw two isomeric structures of Butene ().

    0 marks
  2. (ii)

    Name the following compounds: (I) a three-carbon chain with all single bonds, with a chlorine atom attached to the terminal carbon (structural formula, H atoms shown on each carbon); (II) a four-carbon chain with a carbonyl group (C=O) on the third carbon, with all single bonds otherwise (structural formula).

    0 marks
  3. (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.

    0 marks

Figure in the paper: Structural formulas (condensed/expanded) of compounds (I) and (II) as printed: (I) H–C–C–C–Cl with all hydrogens shown; (II) H–C–C–C(=O)–C–H with all hydrogens shown and the C=O double bond between the third carbon and O. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

For isomers of butene, change the position of the double bond or branch the chain.

Hint 2

Name compounds by chain length + functional group: 'chloro' prefix, '-one' suffix for a ketone.

Hint 3

Recall the oxidising agents for alcohols, the catalyst for adding H₂, and the catalyst for forming esters.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. (i) Isomer 1, but-1-ene: (H–C=C double bond at the end of the 4-carbon chain, all H shown).

    ½ mark

  2. (i) Isomer 2, but-2-ene: . (2-Methylpropene, , is also acceptable.)

    ½ mark

  3. (ii) (I) : chloropropane (1-chloropropane).

    ½ mark

  4. (ii) (II) : butanone (butan-2-one). The C=O is on carbon 2 when the chain is numbered from the nearer end.

    ½ mark

  5. (iii) (I) Oxidation of ethanol: . Condition: heating with an oxidising agent (alkaline or acidified ).

    1 mark

  6. (iii) (II) Hydrogenation of propene: . Condition: presence of a nickel or palladium catalyst.

    1 mark

  7. (iii) (III) Esterification: . Condition: warming in the presence of an acid catalyst (conc. sulphuric acid).

    1 mark

Answer: (i) But-1-ene CH₂=CHCH₂CH₃ and but-2-ene CH₃CH=CHCH₃; (ii) (I) chloropropane, (II) butanone (butan-2-one); (iii) ethanol → ethanoic acid (alk. KMnO₄, heat); propene + H₂ → propane (Ni/Pd); ethanoic acid + ethanol → ethyl ethanoate + water (acid catalyst)

Where the marks are

  • Any two correct isomers of butene (½ + ½ marks)
  • Chloropropane (½ mark)
  • Butanone / butan-2-one (½ mark)
  • Oxidation of ethanol to ethanoic acid with oxidising agent and heat (1 mark)
  • Hydrogenation of propene with Ni/Pd catalyst (1 mark)
  • Esterification with acid catalyst (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Carbon and its Compounds, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 31/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.