Lithium only forms monoxide when heated in oxygen. Sodium forms monoxide and peroxide in excess of oxygen. Other alkali metals form superoxide metals superoxide with oxygen i.e., `MO_(2)`. The abnormal behaviour of lithium is due to small size. The larger size of higher metals also decides the role in formation of superoxide. All the three anions abstract proton from water. The three anions are raleted to each other as follows:
`underset("oxide ion")(O_(2)^(2-)overset((1)/(2)O_(2))(to)underset("peroxide ion")(O_(2)^(2-))overset(O_(2))(to)underset("superoxide ion")(2O_(2)^(-))`
Q. Consider the following reaction :
`M+O_(2) to MO_(2)`
(M=alkali metal) (stable superoxide)

Options

A. M can not be Li and Na
B. M can not be Cs and Rb
C. M can not be Li and Rb
D. None of these

Explanation

To solve the question regarding the alkali metals and their reactions with oxygen, we need to analyze the behavior of each alkali metal in relation to the formation of superoxides.

### Step-by-Step Solution:

1. **Understanding Alkali Metals and Their Oxides**:
- Alkali metals (Li, Na, K, Rb, Cs) react with oxygen to form oxides, peroxides, and superoxides.
- Lithium (Li) primarily forms lithium oxide (Li2O) when heated in oxygen.
- Sodium (Na) can form sodium oxide (Na2O) and sodium peroxide (Na2O2) in excess oxygen.

**Hint**: Recall the general behavior of alkali metals with oxygen, focusing on lithium and sodium.

2. **Formation of Superoxides**:
- For the heavier alkali metals (K, Rb, Cs), they form superoxides (MO2) when reacting with oxygen.
- This is due to their larger ionic size, which allows them to stabilize the superoxide ion (O2^-).

**Hint**: Consider how the size of the metal ion affects its ability to stabilize different types of oxides.

3. **Analyzing the Reaction**:
- The reaction given is: M + O2 → MO2, where M is an alkali metal that forms a stable superoxide.
- Since lithium only forms monoxide and sodium does not form stable superoxides, they cannot be represented by M in this reaction.

**Hint**: Identify which alkali metals can form stable superoxides based on their known reactions with oxygen.

4. **Evaluating the Options**:
- Option 1: M cannot be lithium and sodium. (Correct, as neither forms stable superoxides)
- Option 2: M cannot be cesium and rubidium. (Incorrect, as both can form superoxides)
- Option 3: M cannot be lithium and rubidium. (Incorrect, as rubidium can form superoxides)
- Option 4: None of these. (Incorrect, as option 1 is valid)

**Hint**: Cross-check each option against the known behaviors of the alkali metals.

5. **Conclusion**:
- The correct answer is **Option 1: M cannot be lithium and sodium**, since both do not form stable superoxides.

### Final Answer:
**Option 1: M cannot be lithium and sodium.**