`C_(2)H_(5)Br` gives `C_(2)H_(5)CN` on reaction with alcoholic KCN, while with AgCN the major product is `C_(2)H_(5)NC` . The reason is _________.

Options

A. AgCN is electrovalent
B. AgCN is more covalent
C. Ag is more electropositive as compared to K.
D. Ag is noble metal

Answer

To solve the question regarding the reactions of C2H5Br with alcoholic KCN and AgCN, we will analyze the nature of the reagents and the resulting products.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The reactant is C2H5Br (Bromoethane).
- When treated with alcoholic KCN, the product formed is C2H5CN (Ethyl Cyanide).
- When treated with AgCN, the product formed is C2H5NC (Ethyl Isocyanide).

2. **Understand the Nature of KCN and AgCN**:
- KCN is an ionic compound that dissociates in alcoholic solution to form K⁺ and CN⁻ ions.
- AgCN, on the other hand, is predominantly covalent and does not dissociate into ions in the same way.

3. **Reaction with Alcoholic KCN**:
- In the case of KCN, the CN⁻ ion acts as a nucleophile. The negative charge on carbon (C) of CN⁻ allows it to attack the carbon atom of bromoethane (C2H5Br).
- This leads to a nucleophilic substitution reaction where the bromine atom is replaced by the CN group, resulting in the formation of C2H5CN (Ethyl Cyanide).

4. **Reaction with AgCN**:
- In the case of AgCN, since it is covalent, it does not dissociate into ions. Instead, the nitrogen atom in the CN group has a lone pair of electrons and acts as a nucleophile.
- The nitrogen atom attacks the carbon of bromoethane, leading to a nucleophilic substitution where the bromine is replaced by the nitrogen atom, resulting in the formation of C2H5NC (Ethyl Isocyanide).

5. **Conclusion**:
- The key difference in the products arises from the nature of the nucleophile involved in the reaction. In alcoholic KCN, the nucleophile is CN⁻ (with a negative charge on carbon), leading to the formation of a nitrile (C2H5CN). In AgCN, the nucleophile is the nitrogen atom, leading to the formation of an isocyanide (C2H5NC).
- Therefore, the reason for the difference in products is due to the ionic nature of KCN allowing the formation of a carbon-centered nucleophile, while the covalent nature of AgCN leads to a nitrogen-centered nucleophile.

### Final Answer:
The reason is that KCN is ionic and forms a carbon-centered nucleophile (CN⁻), leading to C2H5CN, while AgCN is covalent and forms a nitrogen-centered nucleophile, leading to C2H5NC.