The loss of molecules of water of crystallization to the atmosphere by some crystalline salts is known as

Explanation

Efflorescence is the process where crystalline salts lose their water of crystallization when exposed to the atmosphere. This happens when the vapour pressure of the hydrated salt is higher than the partial pressure of water vapour in the surrounding air. The salt gradually loses water molecules and may crumble into a powdery form on its surface. Common examples include washing soda (Na₂CO₃·10H₂O), which turns into a white powder (Na₂CO₃·H₂O) over time.

Effervescence refers to the rapid release of gas bubbles from a liquid, typically during a chemical reaction — like adding an acid to a carbonate. Phosphorescence is the emission of light by a substance after it has absorbed energy, continuing to glow even after the energy source is removed. Fluorescence is similar but the glow stops immediately once the energy source is taken away. None of these involve the loss of water of crystallization.