The ratio of the partial pressure of a gaseous component to the total vapour pressure of the mixture is equal to :

Options

A. mass of the component
B. mole fraction of the component
C. mass percent of the component
D. molecular mass of the component.

Explanation

To solve the question regarding the ratio of the partial pressure of a gaseous component to the total vapor pressure of the mixture, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definitions**:
- Let \( P_A \) be the partial pressure of component A.
- Let \( P_{total} \) be the total vapor pressure of the mixture.

2. **Write the Ratio**:
- We need to find the ratio \( \frac{P_A}{P_{total}} \).

3. **Use Ideal Gas Law**:
- According to the ideal gas law, the pressure of a gas can be expressed as:
\[ P = \frac{nRT}{V} \]
- For component A, the partial pressure \( P_A \) can be expressed as:
\[ P_A = \frac{n_A RT}{V} \]
- For the total pressure \( P_{total} \), which includes all components (A, B, C, etc.), it can be expressed as:
\[ P_{total} = \frac{n_{total} RT}{V} \]
where \( n_{total} \) is the total number of moles of all components.

4. **Substitute into the Ratio**:
- Now, substituting these expressions into our ratio:
\[ \frac{P_A}{P_{total}} = \frac{\frac{n_A RT}{V}}{\frac{n_{total} RT}{V}} \]

5. **Simplify the Expression**:
- The \( RT \) and \( V \) terms cancel out:
\[ \frac{P_A}{P_{total}} = \frac{n_A}{n_{total}} \]

6. **Identify the Mole Fraction**:
- The ratio \( \frac{n_A}{n_{total}} \) is defined as the mole fraction \( X_A \) of component A:
\[ X_A = \frac{n_A}{n_{total}} \]

7. **Final Result**:
- Therefore, the ratio of the partial pressure of a gaseous component to the total vapor pressure of the mixture is equal to the mole fraction of that component:
\[ \frac{P_A}{P_{total}} = X_A \]

### Conclusion:
The answer to the question is that the ratio of the partial pressure of a gaseous component to the total vapor pressure of the mixture is equal to the mole fraction of that component.

---