Which of the following reactions of `C_2H_5Br` does not represent an example of nucleophilic substitution?

Options

A. `C_(2)H_(5)"Br" + C_(2) H_(5) "SNa" rarr C_(2)H_(5)-S-C_(2)H_(5) + `NaBr
B. `C_(2)H_(5)"Br" + "AgCN" rarr C_(2) H_(5)NC + ` AgBr
C. `C_(2) H_(5)"Br+ 2H" rarr C_(2)H_(6) + ` HBr
D. `C_(2) H_(5) "Br + KOH " rarr C_(2) H_(5) OH` + KBr

Answer

To determine which reaction of ethyl bromide (C2H5Br) does not represent an example of nucleophilic substitution, we will analyze each given reaction step by step.

### Step 1: Understand Nucleophilic Substitution
Nucleophilic substitution involves a nucleophile (which has a lone pair or a negative charge) attacking an electrophile (like an alkyl halide) and replacing a leaving group (like bromide in this case).

### Step 2: Analyze the Reactions
We will go through each option provided in the question.

#### Option 1: C2H5Br + C2H5SnA
- In this reaction, the nucleophile is C2H5SnA.
- The reaction proceeds with the nucleophile attacking the carbon attached to bromine, resulting in the formation of C2H5SC2H5 and releasing NaBr.
- Since a nucleophile is involved and a substitution occurs, this is a nucleophilic substitution reaction.

#### Option 2: C2H5Br + AgCN
- Here, AgCN is involved.
- The nitrogen in CN has a lone pair and acts as a nucleophile.
- The reaction leads to the formation of ethyl isocyanide (C2H5NC) and AgBr.
- This reaction also involves a nucleophile attacking and substituting bromine, making it a nucleophilic substitution.

#### Option 3: C2H5Br + H2
- In this reaction, hydrogen (H2) is involved.
- There is no nucleophile present since H2 has no lone pair or negative charge.
- The reaction produces ethane (C2H6) and HBr, but since H2 does not act as a nucleophile, this reaction does not represent nucleophilic substitution.

#### Option 4: C2H5Br + KOH
- In this case, KOH dissociates into K+ and OH-.
- The hydroxide ion (OH-) acts as a nucleophile and attacks the carbon in ethyl bromide, leading to the formation of ethanol (C2H5OH) and KBr.
- This is a nucleophilic substitution reaction.

### Conclusion
After analyzing all the options, the reaction that does not represent an example of nucleophilic substitution is:
**Option 3: C2H5Br + H2.**