Of the following reactions, how many reaction, are used for the preparation of amines?
`R - CH_2 - NO_2 overset(H_(2) , Ni) (to) `

Explanation

To determine how many reactions are used for the preparation of amines from the given reaction, we will analyze the reaction step by step.

### Step-by-Step Solution:

1. **Identify the Reaction**: The reaction provided is:
\[ R - CH_2 - NO_2 \overset{(H_2, Ni)}{\rightarrow} \text{amine} \]
Here, \( R - CH_2 - NO_2 \) is an alkyl nitro compound.

2. **Understanding the Reactants**: The reactant \( R - CH_2 - NO_2 \) contains a nitro group (\(-NO_2\)) attached to an alkyl group. The presence of the nitro group indicates that this compound can be reduced to form an amine.

3. **Catalytic Reduction**: The reaction involves catalytic reduction using hydrogen gas (\(H_2\)) and a nickel catalyst (Ni). This process reduces the nitro group to an amine group (\(-NH_2\)).

4. **Reaction Mechanism**: When the nitro compound is treated with hydrogen in the presence of a catalyst, the nitro group is converted to an amine. For example, if we take \( R = CH_3 \) (methyl group), the reaction would be:
\[ CH_3 - CH_2 - NO_2 + 3H_2 \overset{Ni}{\rightarrow} CH_3 - CH_2 - NH_2 + 2H_2O \]
This results in the formation of ethyl amine (\(CH_3 - CH_2 - NH_2\)).

5. **Conclusion**: Since the reaction effectively converts a nitro compound into an amine, we conclude that this reaction is indeed used for the preparation of amines.

### Final Answer:
**1 reaction is used for the preparation of amines.**

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