Some of the hydrated crystals are efflorescent . How do you account for this ?

Explanation

### Step-by-Step Solution:

1. **Understanding Efflorescence**:
- Efflorescent substances are those hydrated crystals that lose their water of crystallization when exposed to air. This process can be observed in certain salts that contain water molecules within their crystalline structure.

2. **Mechanism of Water Loss**:
- When these hydrated crystals are exposed to the atmosphere, they tend to lose water molecules. This occurs because the vapor pressure of the water in the hydrated crystal is greater than the vapor pressure of the water vapor present in the surrounding air (atmospheric humidity).

...