`CH_(3)-CH=CH-CHO overset(A)to CH_(3)-CH=CH-CH_(3)`
The best suitable reagent A is

Options

A. `C_(3)H_(8)S_(2)//H_(2)//Ni`
B. `N_(2)H_(4)//KOH`
C. `Zn-Hg//conc.HCl`
D. HI/P(red)

Answer

To solve the problem, we need to identify the best suitable reagent (A) that converts the compound CH₃-CH=CH-CHO into CH₃-CH=CH-CH₃.

### Step-by-Step Solution:

1. **Identify the Reactant and Product:**
- The reactant is CH₃-CH=CH-CHO (an aldehyde with a double bond).
- The product is CH₃-CH=CH-CH₃ (an alkene).

2. **Analyze the Functional Groups:**
- In the reactant, we have a carbonyl group (C=O) as part of the aldehyde (CHO).
- In the product, this carbonyl group is converted to a methylene group (CH₂), indicating a reduction of the carbonyl group.

3. **Determine the Type of Reaction:**
- The conversion of the carbonyl group (CHO) to a methylene group (CH₂) is a reduction reaction.
- There are two common methods for reducing carbonyl groups: Clemensen reduction and Wolff-Kishner reduction.

4. **Clemensen Reduction:**
- This method involves using zinc amalgam and hydrochloric acid (Zn/HCl).
- However, this method is not suitable here because it is acid-sensitive and can affect the alkene present in the reactant.

5. **Wolff-Kishner Reduction:**
- This method uses hydrazine (N₂H₄) in the presence of a strong base like potassium hydroxide (KOH).
- This method is suitable for reducing aldehydes and ketones to alkanes without affecting double bonds.

6. **Conclusion:**
- Since the reactant contains an alkene that is sensitive to acid, the Wolff-Kishner reduction is the appropriate choice to convert the aldehyde to an alkane while preserving the alkene.
- Therefore, the best suitable reagent (A) is N₂H₄ in the presence of KOH.

### Final Answer:
The best suitable reagent (A) is **N₂H₄ in the presence of KOH** (Wolff-Kishner reduction).