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Question: Answered & Verified by Expert
Assertion : The water pouch of instant cold pack for treating athletic injuries breaks when squeezed and $\mathrm{NH}_4 \mathrm{NO}_3$ dissolves lowering the temperature.
Reason : Addition of non-volatile solute into solvent results into depression of freezing point of solvent.
ChemistrySolutionsAIIMSAIIMS 2006
Options:
  • A If both assertion and reason are true and reason is the correct explanation of the assertion
  • B If both assertion and reason are true but reason is not the correct explanation of the assertion
  • C If assertion is true, but reason is false
  • D Both assertion and reason are false statements.
Solution:
1033 Upvotes Verified Answer
The correct answer is: If both assertion and reason are true and reason is the correct explanation of the assertion
Freezing point of a substance is defined as the temperature at which the vapour pressure of its liquid is equal to the vapour pressure of the corresponding solid. Since the addition of a non-volatile solute always lowers the vapour pressure of solvent, therefore it will be in equilibrium with solid phase at a lower pressure and hence at a lower temperature.

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