Given below are two statements: one is labelled as Assertion and the other is labelled as Reason. Assertion: At 10°C,…
Solutions · Class 12 · JEE Main Previous Year Question
Given below are two statements: one is labelled as Assertion and the other is labelled as Reason.
Assertion: At 10°C, the density of a 5 M solution of KCl [atomic masses of K & Cl are 39 & 35.5 g mol⁻¹ respectively], is 'x' g mL⁻¹. The solution is cooled to −21°C. The molality of the solution will remain unchanged.
Reason: The molality of a solution does not change with temperature as mass remains unaffected with temperature.
In the light of the above statements, choose the correct answer from the options given below.
- a
Assertion is true but Reason is false.
- b
Assertion is false but Reason is true.
- c✓
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
- d
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Strategy:\n> Compare concentration terms based on their dependency on volume. Volume changes with temperature (expansion/contraction), but mass remains constant.\n\nStep 1: Evaluate the Assertion\nThe assertion states that cooling a solution from 10°C to −21°C leaves the molality unchanged. Molality is defined as:\n\nSince neither moles nor mass are affected by temperature, the molality indeed remains constant. Thus, the Assertion is True.\n\nStep 2: Evaluate the Reason\nThe reason explains that molality doesn't change with temperature because mass is temperature-independent. This is the scientifically accurate explanation for why molality is used in thermodynamics. The Reason is True.\n\nConclusion:\nBoth statements are true, and the Reason provides the correct explanation for the Assertion.\n\n
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