The density of air is 0.001293 gm/ml at S.T.P. It’s vapour density is -

Options

A. `10.0gm`
B. `15.0gm`
C. `1.44gm`
D. `14.4gm`

Explanation

To find the vapor density of air given its density at standard temperature and pressure (S.T.P.), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Data:**
- Density of air at S.T.P = 0.001293 g/ml
- Standard molar volume of a gas at S.T.P = 22.4 L = 22,400 ml

2. **Calculate the Mass of Air:**
- Use the formula for mass:
\[ \text{Mass} = \text{Density} \times \text{Volume} \]
- Substitute the values:
\[ \text{Mass} = 0.001293 \, \text{g/ml} \times 22,400 \, \text{ml} \]
- Calculate the mass:
\[ \text{Mass} = 0.001293 \times 22,400 = 28.96 \, \text{g} \]

3. **Determine the Molecular Mass of Air:**
- The mass calculated (28.96 g) represents the molecular mass of air.

4. **Calculate the Vapor Density:**
- The vapor density is defined as half of the molecular mass:
\[ \text{Vapor Density} = \frac{\text{Molecular Mass}}{2} \]
- Substitute the molecular mass:
\[ \text{Vapor Density} = \frac{28.96 \, \text{g}}{2} = 14.48 \, \text{g} \]

5. **Final Answer:**
- The vapor density of air is approximately **14.4 g**.