Among the following which metal forms superoxides of type `MO_2` ?

Options

A. K
B. Rb
C. Cs
D. All of these

Answer

To determine which metals form superoxides of the type \( MO_2 \), we need to analyze the properties of the alkali metals provided in the options: potassium (K), rubidium (Rb), and cesium (Cs).

### Step-by-Step Solution:

1. **Identify the Group of Metals**:
- The metals in the options (K, Rb, Cs) belong to the alkali metals group (Group 1) of the periodic table.

2. **Understanding Oxide Formation**:
- Alkali metals can form different types of oxides when they react with oxygen:
- Lithium (Li) forms lithium oxide (\( Li_2O \)).
- Sodium (Na) forms sodium peroxide (\( Na_2O_2 \)).
- Potassium (K), rubidium (Rb), and cesium (Cs) can form superoxides (\( KO_2, RbO_2, CsO_2 \)).

3. **Superoxide Formation**:
- Superoxides are characterized by the presence of the superoxide ion (\( O_2^- \)).
- Potassium, rubidium, and cesium are large enough to stabilize the superoxide ion due to their larger ionic sizes, which allows for favorable lattice energy when combined with the superoxide ion.

4. **Conclusion**:
- Since potassium, rubidium, and cesium all form superoxides, the correct answer to the question is that all of these metals (K, Rb, Cs) form superoxides of the type \( MO_2 \).
- Therefore, the correct option is **4. All of these**.

### Final Answer:
**The metals that form superoxides of type \( MO_2 \) are potassium, rubidium, and cesium. Hence, the answer is option 4: All of these.**