In the reaction
`CH-= CHoverset(Na//NH_3//(l))(rarr)(A)overset(DCI)(rarr)(B)overset((i)Sia_2BH)(rarr)(C )`.
The product 'C' is

Options

A. `D - C -= C - D`
B. `CH_3-overset(O)overset(||)(C )-H`
C.
D.

Answer

To solve the question step by step, we will analyze the reactions involved:

1. **Identify the starting material**: The starting material is ethyne, which has the formula \( \text{CH} \equiv \text{CH} \).

2. **First Reaction**: The first reaction involves the reduction of ethyne with sodium (Na) in liquid ammonia (NH₃). This reaction is a reduction that converts the alkyne to an alkene.
\[ \text{CH} \equiv \text{CH} \xrightarrow{\text{Na/NH}_3} \text{CH}_2=\text{CH}_2 \]
The product formed (A) is ethylene (or ethene).

3. **Second Reaction**: The product from the first reaction (ethylene) then reacts with DCl (deuterium chloride). This reaction will add deuterium across the double bond of ethylene.
\[ \text{CH}_2=\text{CH}_2 \xrightarrow{\text{DCl}} \text{CH}_2\text{D}-\text{CH}_2\text{D} \]
The product (B) will be a deuterated ethane.

4. **Third Reaction**: The product from the second reaction then reacts with Sia₂BH (diisobutylborane). This reagent is used for hydroboration, which adds boron across the double bond.
\[ \text{CH}_2\text{D}-\text{CH}_2\text{D} \xrightarrow{\text{Sia}_2\text{BH}} \text{CH}_3\text{C}(\text{D})\text{BH}_2 \]
After hydroboration, the next step typically involves oxidation (not shown in the question but implied) which would convert the boron compound to an alcohol.
\[ \text{CH}_3\text{C}(\text{D})\text{BH}_2 \xrightarrow{\text{H}_2\text{O}_2/\text{OH}^-} \text{CH}_3\text{C}(\text{D})\text{OH} \]
The final product (C) is an alcohol, specifically ethanol (or deuterated ethanol if we consider the deuterium).

5. **Final Product**: Thus, the final product (C) is ethanol, represented as \( \text{CH}_3\text{CH}_2\text{OH} \).

### Summary of Steps:
- Step 1: Start with ethyne \( \text{CH} \equiv \text{CH} \).
- Step 2: Reduce with Na/NH₃ to form ethylene \( \text{CH}_2=\text{CH}_2 \).
- Step 3: React with DCl to form deuterated ethane.
- Step 4: Hydroboration with Sia₂BH leads to a boron compound.
- Step 5: Oxidation gives the final product, ethanol \( \text{CH}_3\text{CH}_2\text{OH} \).