The correct option is B If both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
Salt is amphiprotic. This means that it absorbs moisture from around it. This will be in sunny weather if it is humid. When the weather is inclement the relative humidity will be very high and so the salt becomes moist. Heating the salt will get rid of the moisture.
Sodium chloride is hygroscopic, which is why salt cellars / salt shakers become jammed as it sticks together in humid weather.
Hygroscopic means it absorbs water but doesn't dissolve. But seen by holding a woollen sweater in front of an electric fire. Wool is hygroscopic.
When it is deliquescent ( note not deliquesent) the substance absorbs moisture and actually dissolves in it. Eg copper nitrate. Thus both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
Thus Option B is correct.