Step 1: Diazotization of Aniline
Aniline (\( C_6H_5NH_2 \)) reacts with sodium nitrite (\( NaNO_2 \)) and hydrochloric acid (\( HCl \)) at low temperatures (273 - 278 K), forming benzene diazonium chloride (\( C_6H_5N_2Cl \)).
Step 2: Sandmeyer Reaction - Cyanation
Benzene diazonium chloride reacts with copper(I) cyanide (\( CuCN \)) and potassium cyanide (\( KCN \)), replacing the diazonium group with cyano (-CN) group, forming benzonitrile (\( C_6H_5CN \)).
Step 3: Hydrolysis to Benzoic Acid
Benzonitrile undergoes acidic hydrolysis using \( H_3O^+ \) (aqueous acid), converting the cyano (-CN) group into a carboxyl (-COOH) group, forming benzoic acid (\( C_6H_5COOH \)).
Conclusion
Thus, the correct answer is:
\[
\text{NaNO}_2 / \text{HCl}, 273 - 278 K; \text{CuCN} / \text{KCN}; \text{H}_3\text{O}^+
\]