Amongst the compounds given, the one that would form a brilliant coloured dye on treatment with NaNO2 in dil. HCI followed by addition to an alkaline solution of β- naphthol is

As we know, benzenediazonium salt forms brilliant coloured dye with β- naphthol, the compound under consideration must be p-toluidine (c) as it is a primary aromatic amine.Primary aromatic amine, on treatment with NaNO2 in dil. HCI forms the corresponding diazonium chloride salt.