Which of the following will form superoxide?

Options

A. K
B. Na
C. Mg
D. Ca

Answer

To determine which of the given elements will form superoxide, we need to analyze the behavior of alkali metals and alkaline earth metals in relation to oxygen.

### Step-by-Step Solution:

1. **Identify the Elements**: The options provided are:
- Option 1: Potassium (K)
- Option 2: Sodium (Na)
- Option 3: Magnesium (Mg)
- Option 4: Calcium (Ca)

2. **Understand Superoxide Formation**: Superoxides are compounds that contain the superoxide ion (O₂⁻). The general formula for superoxide formation with metals is MO₂, where M is the metal.

3. **Analyze Alkali Metals**:
- **Lithium (Li)**: Forms normal oxide (Li₂O).
- **Sodium (Na)**: Forms peroxide (Na₂O₂).
- **Potassium (K)**: Forms superoxide (KO₂).
- **Rubidium (Rb) and Cesium (Cs)**: Also form superoxides.

4. **Analyze Alkaline Earth Metals**:
- **Beryllium (Be) and Magnesium (Mg)**: These metals are kinetically inert towards oxygen, meaning they do not react with oxygen due to the formation of a protective oxide layer on their surface.
- **Calcium (Ca)**: Reacts with oxygen to form normal oxide (CaO).

5. **Conclusion**: From the analysis:
- Potassium (K) is the only metal among the options that forms superoxide (KO₂).
- Sodium (Na) forms peroxide, and Magnesium (Mg) and Calcium (Ca) do not form superoxides.

Thus, the correct answer is **Potassium (K)**.

### Final Answer:
**Potassium (K) will form superoxide.**