Which one of the alkali metal forms only, the normal oxide, `M_(2)O` ?

Options

A. Li
B. Na
C. K
D. Rb

Explanation

To solve the question of which alkali metal forms only the normal oxide \( M_2O \), we can follow these steps:

### Step 1: Understand the Oxides of Alkali Metals
Alkali metals are known to form various types of oxides, including normal oxides, peroxides, and superoxides. A normal oxide has the formula \( M_2O \), where \( M \) is the alkali metal.

### Step 2: Identify the Alkali Metals
The alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

### Step 3: Analyze the Oxides of Each Alkali Metal
- **Lithium (Li)**: Forms lithium oxide \( Li_2O \) (normal oxide).
- **Sodium (Na)**: Can form sodium oxide \( Na_2O \) (normal oxide) but also forms sodium peroxide \( Na_2O_2 \) and superoxide \( NaO_2 \).
- **Potassium (K)**: Forms potassium oxide \( K_2O \) (normal oxide), potassium peroxide \( K_2O_2 \), and superoxide \( KO_2 \).
- **Rubidium (Rb)**: Similar to potassium, it forms rubidium oxide \( Rb_2O \), rubidium peroxide \( Rb_2O_2 \), and superoxide \( RbO_2 \).
- **Cesium (Cs)**: Forms cesium oxide \( Cs_2O \), cesium peroxide \( Cs_2O_2 \), and superoxide \( CsO_2 \).

### Step 4: Conclusion
From the analysis, we observe that lithium is the only alkali metal that forms only the normal oxide \( Li_2O \) without forming peroxides or superoxides.

### Final Answer
The alkali metal that forms only the normal oxide \( M_2O \) is **Lithium (Li)**.

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