Q76 / 180 · AIIMS 2003 · Chemistry

Assertion : Increasing pressure on pure water decreases its freezing point. Reason : Density of water is minimum at $273 \mathrm{~K}$.

  • A
    If both assertion and reason are true and the reason is the correct explanation of the assertion
  • Correct answer
    B
    If both assertion and reason are true and the reason is not the correct explanation of the assertion
  • C
    If assertion is true but reason is false
  • D
    If both assertion and reason are false.

Solution

According to Clapeyron-Clausius equation, $\frac{d T}{d P}=\frac{T\left(V_l-V_s\right)}{\Delta H_f}$ Since density of ice is less than that of water, $V_s$ is greater than $V_l$. In other words, the expression on the right hand side of the above equation is negative. This means that the increase of pressure must lower and decrease of pressure must raise the freezing point.

Hence, the correct answer is option: 'B'.

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