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Science — CBSE Class 10 board question

Q1. [1]
Assertion (A) : It is advised that while diluting an acid one should add water to acid and not acid to water keeping the solution continuously stirred. Reason (R) : The process of dissolving an acid into water is highly exothermic.
  1. (a) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of (A).
  2. (b) Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of (A).
  3. (c) Assertion (A) is true, but Reason (R) is false.
  4. (d) Assertion (A) is false, but Reason (R) is true.
Previously asked in CBSE board exam
2023 31/6/1 Q17
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding rag
Model Answer

(d) Assertion (A) is false, but Reason (R) is true.

The correct practice is to add acid to water (not water to acid). So Assertion (A) is false. The Reason (R) is true — dissolving acid in water is highly exothermic.

Explanation

The textbook (Chapter 2, Activity 2.10) clearly states: "The acid must always be added slowly to water with constant stirring." The Assertion incorrectly reverses this — it says "add water to acid," which is the dangerous practice. The Reason is correctly stated (the process is highly exothermic). Hence, A is false but R is true → option (d).

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