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(i) Carbon cannot form C^4+… (Class 10 Science 2026, Q29A)

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ScienceCBSE Class 10 · Board exam 2026, set 31/4/1 · 5 marks · Short answer

CBSE Class 10 Science 2026: question 29(A)

Set in the CBSE Class 10 board exam of 2026, paper 31/4/1, section B, question 29(A), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q29(A) · 5 marks · Short answerCarbon and its Compounds

(i) Carbon cannot form cation and anion. Explain.
(ii) Define homologous series of carbon compounds. Why are the melting and boiling points of higher than or ?
(iii) What happens when ethanol is heated with acidified potassium dichromate?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/4/1.

Hints

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

Hint 1

Count the valence electrons of carbon and the number of protons in its nucleus.

Hint 2

Compare the molar masses of the three alkanes.

Hint 3

Potassium dichromate is an oxidising agent. What does ethanol become when oxidised?

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) Carbon (2, 4) has 4 valence electrons.

    **C:** To form this cation, carbon must lose 4 electrons. That needs a very large amount of energy, so it is energetically not possible.

    1 mark

  2. **C:** To form this anion, carbon must gain 4 electrons. A nucleus with only 6 protons cannot hold 10 electrons. Carbon therefore shares electrons and forms covalent bonds instead.

    1 mark

  3. (ii) Homologous series: a series of carbon compounds that have the same functional group replacing hydrogen in the carbon chain. Successive members differ by a unit (14 u) and have similar chemical properties. Example: .

    1 mark

  4. In a homologous series, melting and boiling points increase as molecular mass increases. (58 u) has a higher molecular mass than (44 u) and (30 u), so its melting and boiling points are higher.

    1 mark

  5. (iii) Acidified potassium dichromate is an oxidising agent. It oxidises ethanol to ethanoic acid, and its orange colour turns green:

    1 mark

Answer: (i) Losing 4 electrons needs too much energy; 6 protons cannot hold 10 electrons. (ii) Same functional group, successive members differ by CH; CH has a higher molecular mass. (iii) Ethanol is oxidised to ethanoic acid.

Where the marks are

  • Explains why C and C cannot form (2 marks)
  • Defines homologous series correctly (1 mark)
  • Gives the higher molecular mass of CH as the reason (1 mark)
  • States that ethanoic acid is formed by oxidation (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 paper2026 board paper, set 31/4/1: 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.