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(i) Name the simplest… (Class 10 Science 2023, Q34b)

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ScienceCBSE Class 10 · Board exam 2023, set 31/2/1 · 5 marks · Long answer

CBSE Class 10 Science 2023: question 34(b)

Set in the CBSE Class 10 board exam of 2023, paper 31/2/1, section D, question 34(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

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

(i) Name the simplest saturated hydrocarbon. Draw its electron dot structure. Which type of bonds exist in this compound ?
(ii) Name any two mixtures of the carbon compound used as a fuel in daily life, of which the above mentioned compound is an important component.
(iii) In which homologous series of carbon compounds can this compound be placed ? Write the general formula of the series.
(iv) Which type of flame is produced on burning it ?

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 31/2/1.

Hints

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

Hint 1

The simplest saturated hydrocarbon has only one carbon atom.

Hint 2

Carbon has 4 valence electrons and each hydrogen has 1. How many pairs must be shared?

Hint 3

Saturated hydrocarbons burn completely. What kind of flame does that give?

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) The simplest saturated hydrocarbon is methane, .

    ½ mark

  2. (i) Electron dot structure (described):

    • Write C at the centre with four H atoms placed above, below, left and right of it.
    • Between C and each H, draw one shared pair of electrons: one electron from carbon (×) and one from hydrogen (•).
    • This gives four shared pairs in total.
    • Carbon then has an octet and each hydrogen has a duplet.
    1 mark

  3. (i) Methane contains four single covalent bonds (C–H).

    ½ mark

  4. (ii) Two fuels containing methane as a major component are biogas and CNG (compressed natural gas).

    1 mark

  5. (iii) Methane belongs to the alkane homologous series.

    ½ mark

  6. (iii) The general formula of the series is .

    ½ mark

  7. (iv) Being saturated, methane burns completely with a clean blue flame that gives no soot.

    1 mark

Answer: (i) Methane, CH₄; four single covalent bonds; (ii) biogas and CNG; (iii) alkanes, CₙH₂ₙ₊₂; (iv) clean blue flame

Where the marks are

  • Names methane (½ mark)
  • Correct electron dot structure (1 mark)
  • Single covalent bonds (½ mark)
  • Biogas and CNG (½ + ½ mark)
  • Alkanes (½ mark)
  • General formula CₙH₂ₙ₊₂ (½ mark)
  • Blue/clean flame (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 paper2023 board paper, set 31/2/1: 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.