Define :

(i) Hygroscopy
(ii) Efflorescence.

(i) The phenomenon by which a substance absorbs moisture from the atmosphere when exposed to it, without changing its state [i.e., a solid substances remains a solid after absorption of moisture] is known as Hygroscopy.

(ii) Crystalline hydrated salts which on exposure to the atmosphere lose their moisture [water of crystallization] partly or completely to the atmosphere and change into the amorphous state are called efflorescent substances and the phenomenon is known as Efflorescence.