The mass of an oxygen atom is half that of a sulphur atom. Can we decide on this basis that the density of sulphur vapour relative to oxygen is 2?
(a) Yes,
(b) No

Answer

To determine whether we can conclude that the density of sulfur vapor relative to oxygen is 2 based on the information that the mass of an oxygen atom is half that of a sulfur atom, we need to analyze the relationship between atomic mass and vapor density.

### Step-by-Step Solution:

1. **Understanding Atomic Mass**:
- The atomic mass of oxygen (O) is approximately 16 g/mol.
- The atomic mass of sulfur (S) is approximately 32 g/mol.
- Given that the mass of an oxygen atom is half that of a sulfur atom, this aligns with the atomic masses (16 g/mol for O and 32 g/mol for S).

2. **Molar Mass and Density Relationship**:
- The density (D) of a gas can be expressed using the formula:
\[ D = \frac{m}{V} = \frac{PM}{RT} \]
where \( P \) is pressure, \( M \) is molar mass, \( R \) is the universal gas constant, and \( T \) is temperature.

3. **Relative Density Calculation**:
- To find the relative density of sulfur vapor to oxygen vapor, we can use the molar masses.
- The relative density (RD) of sulfur vapor (S) to oxygen vapor (O) is given by:
\[ RD = \frac{M_S}{M_O} \]
- Substituting the molar masses:
\[ RD = \frac{32 \text{ g/mol}}{16 \text{ g/mol}} = 2 \]

4. **Conclusion**:
- Based on the calculation, the relative density of sulfur vapor to oxygen vapor is indeed 2.
- Therefore, we can conclude that the answer to the question is (a) Yes.