Choose the correct statement(s) among the following .
I. Alkali metal is highly reactive.
II. Alkali metal has lowest ionisation enthalpy among their respective period.
III. Superoxide ions is stable only in the presence of large cations.

Options

A. Only 1
B. II and III
C. II and III
D. All of the above

Answer

To solve the question, we need to analyze each statement regarding alkali metals and superoxide ions.

### Step-by-Step Solution:

1. **Analyzing Statement I**:
- **Statement**: "Alkali metal is highly reactive."
- **Explanation**: Alkali metals (Li, Na, K, Rb, Cs, Fr) are known for their high reactivity. This is due to their large atomic size and low ionization energy, which allows them to easily lose their outermost electron.
- **Conclusion**: This statement is **correct**.

2. **Analyzing Statement II**:
- **Statement**: "Alkali metal has lowest ionisation enthalpy among their respective period."
- **Explanation**: Alkali metals have the lowest ionization energies in their respective periods because they have only one electron in their outermost shell. This makes it easier to remove that electron compared to other elements in the same period, which have more electrons and a stronger effective nuclear charge.
- **Conclusion**: This statement is **correct**.

3. **Analyzing Statement III**:
- **Statement**: "Superoxide ions are stable only in the presence of large cations."
- **Explanation**: Superoxide ions (O₂⁻) are indeed stable when associated with larger cations like K⁺, Rb⁺, and Cs⁺. The larger size of these cations helps stabilize the superoxide ion due to the lower charge density, which reduces the repulsion between the superoxide ion and the cation.
- **Conclusion**: This statement is **correct**.

### Final Conclusion:
Since all three statements are correct, the answer to the question is that all of the statements are true.

### Answer:
**All of the above statements are correct.**