`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 question regarding the conversion of the compound \( CH_3-CH=CH-CHO \) to \( CH_3-CH=CH-CH_3 \), we need to identify the best suitable reagent \( A \) that facilitates this transformation. The aldehyde group (CHO) needs to be removed and replaced with a hydrogen atom, effectively converting the aldehyde into an alkene.

### Step-by-Step Solution:

1. **Identify the Functional Groups**:
- The starting compound \( CH_3-CH=CH-CHO \) contains an aldehyde group (CHO) at the end of the carbon chain.
- The target compound \( CH_3-CH=CH-CH_3 \) is an alkene with no functional groups.

2. **Understand the Reaction Type**:
- The transformation involves the reduction of the aldehyde group to a methylene group (–CH2–), which is characteristic of a reduction reaction.

3. **Select the Appropriate Reagent**:
- The reagent that can effectively convert an aldehyde to a corresponding alkane is the Wolff-Kishner reduction reagent, which involves hydrazine (\( N_2H_4 \)) followed by a strong base like potassium hydroxide (KOH) in the presence of ethylene glycol.

4. **Write the Reaction Mechanism**:
- The hydrazine reacts with the aldehyde to form a hydrazone intermediate.
- Upon heating with KOH and ethylene glycol, nitrogen gas (\( N_2 \)) is eliminated, resulting in the formation of the alkene.

5. **Conclusion**:
- The best suitable reagent \( A \) for this transformation is \( N_2H_4 \) (hydrazine) followed by KOH in ethylene glycol.

### Final Answer:
The best suitable reagent \( A \) is \( N_2H_4 \) (hydrazine) followed by KOH in ethylene glycol.