Under what pressure conditions `CuSO_(4).5H_(2)O` be efforescent at `25^(@)C`. How good a drying agent is `CuSO_(4).3H_(2)O` at the same temperature? Given
`CuSO_(4).5H_(2)O(s) hArr CuSO_(4).3H_(2)O(s)+2H_(2)O(v)`
`K_(p)=1.086xx10^(-4) atm^(2)` at `25^(@)C`. Vapour pressure of water at `25^(@)C` is `23.8` mm of Hg.

Explanation

To solve the given problem, we need to analyze the equilibrium reaction and the conditions under which `CuSO4.5H2O` becomes efflorescent at `25°C`. We will also evaluate how effective `CuSO4.3H2O` is as a drying agent at the same temperature.

### Step-by-Step Solution:

1. **Understanding Efflorescence**:
- Efflorescence occurs when a hydrated salt loses water to the atmosphere, usually due to low humidity conditions. For `CuSO4.5H2O`, this means it will lose water molecules and convert to `CuSO4.3H2O`.

2. **Equilibrium Reaction**:
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