When a salt loses its water of crystallization to the atmosphere on exposure, the process is said to be

The process of a salt losing its water of crystallization to the atmosphere on exposure is known as efflorescence. This happens when a hydrate salt is exposed to a dry atmosphere, causing the water molecules in the crystal lattice to evaporate, leaving behind the anhydrous salt. This process can be reversed by adding water to the anhydrous salt to form the hydrate again. The other options are not relevant to this process: deliquescence refers to a process where a substance absorbs water from the atmosphere and dissolves in it; effervescence refers to the escape of gas from a liquid or a solid due to a chemical reaction, and fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.