The correct relationship between molecular mass (M) and vapour (VD) is

Options

A. VD = 2 M
B. `VD = (M)/(2)`
C. VD = `M^(2)`
D. M = `(VD)^(1/2)`

Answer

To find the correct relationship between molecular mass (M) and vapor density (VD), we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Vapor Density (VD)**:
- Vapor density is defined as the mass of a certain volume of a gas compared to the mass of an equal volume of hydrogen gas (H₂) at the same temperature and pressure.

2. **Mathematical Representation**:
- The formula for vapor density can be expressed as:
\[ VD = \frac{\text{mass of gas}}{\text{mass of equal volume of hydrogen}} \]

3. **Molecular Mass of Hydrogen**:
- The molecular mass of hydrogen (H₂) is 2 g/mol (since each hydrogen atom has a mass of approximately 1 g/mol).

4. **Relating Vapor Density to Molecular Mass**:
- If we denote the molecular mass of the gas as M, we can express the vapor density as:
\[ VD = \frac{M}{\text{molecular mass of hydrogen}} \]
- Substituting the molecular mass of hydrogen (2 g/mol) into the equation gives:
\[ VD = \frac{M}{2} \]

5. **Rearranging the Equation**:
- To express molecular mass in terms of vapor density, we can rearrange the equation:
\[ M = 2 \times VD \]

6. **Conclusion**:
- Thus, the correct relationship between molecular mass (M) and vapor density (VD) is:
\[ VD = \frac{M}{2} \]
- This means that vapor density is equal to the molecular mass divided by 2.

### Final Answer:
The correct relationship is:
\[ VD = \frac{M}{2} \]