Concept:Efflorescence is the loss of water of crystallization when a hydrated salt is exposed to air.
Explanation:The initial mass of the salt is
2g.
After exposure to the atmosphere, its mass drops to
1.5g.
This decrease in mass shows that the salt has lost moisture to the surroundings.
A hydrated salt loses its water of crystallization spontaneously when its vapour pressure exceeds that of water vapour in the air.
This process is called efflorescence.
It is different from hygroscopy or deliquescence, both of which involve gaining moisture from the air, not losing it.
Answer:C. efflorescence