Addition of `1` mol of `B` of `8` mole of `A` increases vapour pressure of `A`. If `A` and `B` form ideal soltion, then

Options

A. `A` is more volatile than `B`
B. `B` is more volatile than `A`
C. volatility cannot be predicted on the basis of the given data
D. Lower boiling azeotrope will be formed

Explanation

To solve the problem, we need to analyze the effect of adding 1 mole of substance B to 8 moles of substance A on the vapor pressure of A, given that A and B form an ideal solution.

### Step-by-Step Solution:

1. **Understanding Vapor Pressure and Ideal Solutions**:
- The vapor pressure of a component in an ideal solution is determined by Raoult's Law, which states that the partial vapor pressure of a component in the solution is equal to the vapor pressure of the pure component multiplied by its mole fraction in the solution.
- For component A, the partial vapor pressure \( P_A \) can be expressed as:
\[ P_A = P_{A}^0 \cdot X_A \]
- Where \( P_{A}^0 \) is the vapor pressure of pure A and \( X_A \) is the mole fraction of A in the solution.

2. **Calculating Mole Fractions**:
- Initially, we have 8 moles of A and we add 1 mole of B. The total number of moles in the solution becomes:
\[ \text{Total moles} = 8 + 1 = 9 \text{ moles} \]
- The mole fraction of A (\( X_A \)) is:
\[ X_A = \frac{8}{9} \]
- The mole fraction of B (\( X_B \)) is:
\[ X_B = \frac{1}{9} \]

3. **Determining the Change in Vapor Pressure**:
- When we add B, the vapor pressure of A increases. This implies that the partial vapor pressure of A after the addition can be calculated as:
\[ P_A' = P_{A}^0 \cdot X_A' = P_{A}^0 \cdot \frac{8}{9} \]
- The vapor pressure of B (\( P_B \)) is higher than that of A, indicating that B is more volatile than A.

4. **Conclusion**:
- Since the addition of B increases the vapor pressure of A, it can be concluded that the vapor pressure of pure component B (\( P_B^0 \)) is greater than that of pure component A (\( P_A^0 \)). Therefore, we can state:
\[ P_B^0 > P_A^0 \]
- This means that B is more volatile than A.

### Final Answer:
The correct conclusion is that the vapor pressure of pure component B is greater than that of pure component A, indicating that B is more volatile than A.