Amongst the compounds given, the one that would form a brilliant coloured dye on treatment with NaNO ₂ in dil. HCl followed by addition to an alkaline solution of -naphthol is

Step-by-step solution

As we know, benzenediazonium salt forms brilliant coloured dye with -naphthol, the compound under consideration must be p -toludine (c) as it is a primary aromatic amine. Primary aromatic amine, on treatment with NaNO ₂ in dil. HCl forms the corresponding diazonium chloride salt.