The solid-vapour equilibrium can be represented as
I `I_2(solid) rarr I_2(vapour)`
IIcamphor (solid)` iff `camphor (vapour)
III `NH_4Cl(solid) iff NH_4Cl(vapour)`
Point out the correct option(s).

Options

A. I and II
B. Only II
C. II and III
D. All of the above

Answer

To solve the question regarding solid-vapour equilibrium, we need to analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Solid-Vapour Equilibrium**:
- Solid-vapour equilibrium refers to the state where a solid and its vapour coexist at a certain temperature and pressure. This is typically represented using double arrows (⇌) to indicate that both the forward and reverse processes can occur.

2. **Analyzing Statement I**:
- The first statement is:
\[ I_2(solid) \rightarrow I_2(vapour) \]
- This representation uses a single arrow, which indicates a one-way process. In equilibrium, we need to show that both the solid can turn into vapour and vapour can turn back into solid. Therefore, this representation is incorrect.

3. **Analyzing Statement II**:
- The second statement is:
\[ \text{camphor (solid)} \rightarrow \text{camphor (vapour)} \]
- Similar to the first statement, this also uses a single arrow. For equilibrium, it should be represented as:
\[ \text{camphor (solid)} \rightleftharpoons \text{camphor (vapour)} \]
- Since it uses a single arrow, this representation is also incorrect.

4. **Analyzing Statement III**:
- The third statement is:
\[ NH_4Cl(solid) \rightarrow NH_4Cl(vapour) \]
- Again, this uses a single arrow. The correct representation for equilibrium should be:
\[ NH_4Cl(solid) \rightleftharpoons NH_4Cl(vapour) \]
- Thus, this representation is also incorrect.

5. **Conclusion**:
- After analyzing all three statements, we find that none of them correctly represent solid-vapour equilibrium. Therefore, the correct options are none.

### Final Answer:
- None of the statements correctly represent solid-vapour equilibrium.