Question

Assertion : The water pouch of instant cold pack for treating athletic injuries breaks when squeezed and NH₄NO₃ dissolves thus lowering the temperature.

Reason : Addition of non-volatile solute into solvent results into depression of freezing point of solvent.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

Answer 1

Correct option  (a) Both A and R are true and R is the correct explanation of A

Explanation:

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 nonvolatile 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.