When an alkali metal is reacted with hydrogen then metallic hydride is formed. In this reaction

Options

A. Hydrogen is oxidised
B. Hydrogen is reduced
C. Hydrogen is neither oxidised nor reduced
D. Hydrogen is oxidised as well as reduced

Answer

To solve the question regarding the reaction of an alkali metal with hydrogen to form a metallic hydride, we will analyze the oxidation states of the elements involved and determine whether hydrogen is oxidized, reduced, or neither.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction between an alkali metal (let's denote it as M) and hydrogen (H₂) can be represented as:
\[ 2M + H_2 \rightarrow 2MH \]
Here, \(MH\) is the metallic hydride formed.

2. **Determine Oxidation States**:
- In the reactants:
- The alkali metal (M) is in its elemental form, so its oxidation state is 0.
- Hydrogen (H₂) is also in its elemental form, so its oxidation state is 0.
- In the product:
- The alkali metal (M) in the hydride has an oxidation state of +1.
- The hydrogen in the hydride (MH) has an oxidation state of -1.

3. **Analyze Changes in Oxidation States**:
- For the alkali metal (M):
- Oxidation state changes from 0 (in M) to +1 (in MH).
- This indicates that the metal is losing electrons, which is oxidation.
- For hydrogen:
- Oxidation state changes from 0 (in H₂) to -1 (in MH).
- This indicates that hydrogen is gaining electrons, which is reduction.

4. **Conclusion on Hydrogen's Role**:
- Since hydrogen is gaining electrons, it is being reduced in this reaction.

5. **Evaluate the Options**:
- **Option 1**: Hydrogen is oxidized. (Incorrect)
- **Option 2**: Hydrogen is reduced. (Correct)
- **Option 3**: Hydrogen is neither oxidized nor reduced. (Incorrect)
- **Option 4**: Hydrogen is oxidized as well as reduced. (Incorrect)

Thus, the correct answer is that hydrogen is reduced.

### Final Answer:
The correct option is **Option 2: Hydrogen is reduced**.