a) Efflorescence: The phenomenon in which certain hydrated substances lose their water of crystallization partly or completely when exposed to ordinary atmospheric conditions for sometimes is called as efflorescence.
b) Deliquescence: The phenomenon in which hygroscopic substances absorb moisture from the air to such an extent that they are finally converted into solution form is called deliquescence.
c) Hygroscopic: Those substances which absorb moisture when exposed to ordinary atmospheric conditions are called hygroscopic substances and the phenomenon is called hygroscopy.
d) Water of crystallization: Water associated with crystals as their essential part of constituent is known as water of crystallization.