Vapour pressure of a solvent decreases by 1% on adding a non-volatile solute `Na_2SO_(4)`. If it dissociates up to 25% then determine mole-fraction of solute, if solvent is 5 mole.

Explanation

To solve the problem, we need to determine the mole fraction of the solute \( \text{Na}_2\text{SO}_4 \) when it is added to a solvent, given that the vapor pressure of the solvent decreases by 1% and the solute dissociates by 25%. The solvent is provided in 5 moles.

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Decrease in vapor pressure = 1% of \( P_0 \)
- Degree of dissociation \( \alpha = 25\% = 0.25 \)
- Moles of solvent = 5 moles
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