The vapour pressure of pure solvent is 0.8 mm of Hg at a particular temperature. On addition of a non-volatile solute ‘A’ the vapour pressure of solution becomes 0.6 mm of Hg. The mole fraction of component ‘A’ is:

Options

A. 0.25
B. 0.75
C. 0.5
D. 0.35

Answer

To find the mole fraction of the non-volatile solute 'A', we can use Raoult's law, which relates the vapor pressure of a solution to the vapor pressure of the pure solvent and the mole fraction of the solute.

### Step-by-Step Solution:

1. **Identify the given values:**
- Vapor pressure of pure solvent (P₀) = 0.8 mm Hg
- Vapor pressure of solution (P) = 0.6 mm Hg

2. **Apply Raoult's Law:**
According to Raoult's law, the relative lowering of vapor pressure is given by:
\[ \frac{P₀ - P}{P₀} = X_A \]
where \(X_A\) is the mole fraction of the solute 'A'.

3. **Calculate the relative lowering of vapor pressure:**
Substitute the values into the equation:
\[ \frac{0.8 - 0.6}{0.8} = X_A \]
This simplifies to:
\[ \frac{0.2}{0.8} = X_A \]

4. **Perform the division:**
\[ X_A = 0.25 \]

5. **Conclusion:**
The mole fraction of component 'A' (the solute) is 0.25.

### Final Answer:
The mole fraction of component 'A' is 0.25.

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