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Assertion (A) : When NaCl… (Class 12 Chemistry 2024, Q13)

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ChemistryCBSE Class 12 · Board exam 2024, set 56/1/1 · 1 mark · Assertion-reason

CBSE Class 12 Chemistry 2024: question 13

Set in the CBSE Class 12 board exam of 2024, paper 56/1/1, section A, question 13, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q13 · 1 mark · Assertion-reasonCompetency-basedSolutions

Assertion (A) : When NaCl is added to water a depression in freezing point is observed.
Reason (R) : NaCl undergoes dissociation in water.

  1. (A)Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
  2. (B)Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
  3. (C)Assertion (A) is true, but Reason (R) is false.
  4. (D)Assertion (A) is false, but Reason (R) is true.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 56/1/1.

Hints

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

Hint 1

Would a non-electrolyte also lower the freezing point?

Hint 2

Dissociation changes only the size of the effect.

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. Any non-volatile solute lowers the freezing point of water, so (A) is true. NaCl does dissociate in water, so (R) is also true.

  2. The depression is caused by the presence of solute particles, not by dissociation itself; dissociation only increases its magnitude. So (R) is not the correct explanation of (A).

    1 mark

Answer: Option (B)

Where the marks are

  • Both statements true, but R is not the explanation (1 mark)

Revise the chapter

  • Chapter: Solutions (notes, formulas, where marks are lost and every past question)
Practise this chapterBoard-style questions from Solutions, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 56/1/1: 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.