Vapour density of a gas is 15 . The gas can be

Options

A. Ethane
B. Ozone
C. Ethylene
D. Phosphene

Answer

To solve the problem of identifying the gas with a vapor density of 15, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Vapor Density**:
The vapor density (VD) of a gas is defined as the mass of a certain volume of the gas compared to the mass of an equal volume of hydrogen at the same temperature and pressure. The formula for vapor density is given as:
\[ \text{Vapor Density} = \frac{\text{Molecular Mass}}{2} \]

2. **Setting Up the Equation**:
Given that the vapor density of the gas is 15, we can set up the equation:
\[ 15 = \frac{\text{Molecular Mass}}{2} \]

3. **Calculating Molecular Mass**:
To find the molecular mass (MM) of the gas, we can rearrange the equation:
\[ \text{Molecular Mass} = 15 \times 2 = 30 \text{ g/mol} \]

4. **Identifying the Gases**:
Now we need to check the molecular mass of each of the given options to see which one has a molecular mass of 30 g/mol.

- **Option A: Ethane (C2H6)**:
- Molecular mass = (2 × 12) + (6 × 1) = 24 + 6 = 30 g/mol

- **Option B: Ozone (O3)**:
- Molecular mass = 3 × 16 = 48 g/mol

- **Option C: Ethylene (C2H4)**:
- Molecular mass = (2 × 12) + (4 × 1) = 24 + 4 = 28 g/mol

- **Option D: Phosphine (PH3)**:
- Molecular mass = 31 + (3 × 1) = 31 + 3 = 34 g/mol

5. **Conclusion**:
From the calculations, we can see that only Ethane (C2H6) has a molecular mass of 30 g/mol, which corresponds to the vapor density of 15. Therefore, the gas is:
\[ \text{Answer: Ethane (Option A)} \]