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Give reasons for the… (Class 10 Science 2026, Q29A)

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

CBSE Class 10 Science 2026: question 29(A)

Set in the CBSE Class 10 board exam of 2026, paper 31/5/1, 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 · Long answerMetals and Non-metals

Give reasons for the following :

  1. (i)(I)

    Ionic compound have generally high melting points and boiling points.

    0 marks
  2. (i)(II)

    Solder, an alloy of lead and tin, is used for welding electrical wires.

    0 marks
  3. (i)(III)

    Carbon cannot reduce the oxides of Na or Mg.

    0 marks
  4. (ii)

    The reaction of compound 'X' with aluminium is used to join railway tracks: (I) Identify the compound 'X'. (II) Name the reaction. (III) Write the balanced chemical equation of the reaction of compound 'X' with aluminium.

    2 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/5/1.

Hints

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

Hint 1

Think about the type and strength of forces between ions.

Hint 2

Where do Na, Mg and C lie in reactivity?

Hint 3

Which metal oxide is reduced by aluminium to give molten iron for welding rails?

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)(I) In ionic compounds oppositely charged ions are held by strong electrostatic (inter-ionic) forces; a large amount of energy is needed to break them, so melting and boiling points are high.

    1 mark

  2. (i)(II) Solder has a low melting point, so it melts easily and joins electrical wires without damaging them.

    1 mark

  3. (i)(III) Na and Mg are highly reactive and have more affinity for oxygen than carbon, so carbon cannot remove oxygen from their oxides; they are obtained by electrolytic reduction.

    1 mark

  4. (ii)(I) X is iron(III) oxide, Fe₂O₃.

    ½ mark

  5. (II) The reaction is the thermit reaction.

    ½ mark

  6. (III) – molten iron fills the gap between rails.

    1 mark

Answer: (i) strong inter-ionic forces; low melting point of solder; Na/Mg have greater affinity for oxygen than C. (ii) X = Fe₂O₃; thermit reaction; Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat.

Where the marks are

  • Strong inter-ionic attraction needs much energy (1 mark)
  • Solder has low melting point (1 mark)
  • Na/Mg more reactive / greater affinity for oxygen than carbon (1 mark)
  • X = Fe₂O₃ (½ mark)
  • Thermit reaction (½ mark)
  • Balanced equation (1 mark; ½ deducted if unbalanced)

Revise the chapter

Practise this chapterBoard-style questions from Metals and Non-metals, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/5/1: 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.