Statement - The water pouch of instant cold pack for treating athletic injuries breakes when squeezed and `NH_(4)NO_(3)` dissolves lowering the temperature.
Explanation - Addition of non-volatile solute into solvent results into depression of freezing point of solvent.

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 expalanation of the assertion
C. if assertion is true, reason is false
D. both assertion and reason are false statements.

Answer

a

Explanation

Frezzing 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 fo solvent. therefore it will be in equilibrium with solid phase at a lower pressure and hence at a lower temperature.