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Answer the following. (Science 2025 31/2/1 Q34b)

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ScienceCBSE Class 10 · Board exam 2025, set 31/2/1 · 5 marks · Long answer

CBSE Class 10 Science 2025: question 34(b)

Set in the CBSE Class 10 board exam of 2025, 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

Answer the following.

  1. (i)

    Differentiate between saturated and unsaturated hydrocarbons by giving one example each, with a structural formula.

    0 marks
  2. (ii)

    Write the method of converting an unsaturated hydrocarbon into a saturated hydrocarbon. Name the industry where this reaction is commonly used.

    0 marks
  3. (iii)

    Write the name and structure of a hydrocarbon having double bond and four carbon atoms in its one molecule.

    0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 31/2/1.

Hints

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

Hint 1

Look at the type of bonds between the carbon atoms in each class.

Hint 2

What must be added across a double bond to make it single? What catalyst helps?

Hint 3

For four carbons with one double bond, use the alkene formula with n = 4.

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) Difference: Saturated hydrocarbons have only single covalent bonds between all carbon atoms (general formula , alkanes). Unsaturated hydrocarbons have at least one double or triple bond between two carbon atoms (general formula for alkenes, for alkynes).

    1 mark

  2. (i) **Saturated example – Propane, .** Structural formula: H–C–C–C–H in a chain, with every bond single and each carbon carrying enough H atoms to make 4 bonds. That is, the end carbons have 3 H each and the middle carbon has 2 H.

    1 mark

  3. (i) **Unsaturated example – Propene, .** Structural formula: H₂C=CH–CH₃, with one C=C double bond between C-1 and C-2. Propyne, , is also a correct example.

    1 mark

  4. (ii) Method: Heat the unsaturated hydrocarbon with hydrogen in the presence of a nickel (or palladium) catalyst. This addition of hydrogen is called hydrogenation, e.g. .

    1 mark

  5. (ii) Industry: This reaction is used in the vegetable oil (vanaspati ghee) industry to hydrogenate vegetable oils.

    ½ mark

  6. (iii) **Butene, .** Structure (but-1-ene): , i.e. H₂C=CH–CH₂–CH₃.

    ½ mark

Answer: (i) Saturated: only C–C single bonds, e.g. propane CH₃CH₂CH₃. Unsaturated: at least one C=C or C≡C, e.g. propene CH₂=CH–CH₃. (ii) Hydrogenation (H₂ with Ni/Pd catalyst); used in the vegetable oil (vanaspati) industry. (iii) Butene, CH₂=CH–CH₂–CH₃.

Where the marks are

  • Correct difference between saturated and unsaturated hydrocarbons (1 mark)
  • Saturated example with correct structural formula (1 mark)
  • Unsaturated example with correct structural formula (1 mark)
  • Method: addition of hydrogen with Ni/Pd catalyst (hydrogenation) (1 mark)
  • Industry: hydrogenation of vegetable oils (½ mark)
  • Butene with its structure (½ 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 31/2/1: 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.