1. Identify the reaction with sulphanilic acid

   Sulphanilic acid is $p$-aminobenzenesulphonic acid: $\mathrm{H_2N{-}C_6H_4{-}SO_3H}$

   When an aromatic primary amine is treated with $\mathrm{NaNO_2}$ in acidic medium, it undergoes diazotisation to form a diazonium salt.

   So, $\mathrm{Sulphanilic\ acid + NaNO_2 + CH_3COOH \rightarrow X}$ where $X$ is the corresponding diazonium salt: $\mathrm{[N_2^+{-}C_6H_4{-}SO_3H]}$ i.e. $p$-sulphobenzenediazonium salt.

2. Formation of azo dye

   A diazonium salt couples with activated aromatic compounds such as phenol or aniline in alkaline medium to give an azo dye.

   The usual coupling of diazotised sulphanilic acid gives orange II / methyl orange type azo system, containing the linkage $\mathrm{-N=N-}$ between the diazotised sulphanilic acid ring and the coupling ring.

3. Key structural feature of the dye $Y$

   The product must contain:

   • one benzene ring with $\mathrm{SO_3H}$ group para to the azo linkage origin,
   • an azo linkage $\mathrm{-N=N-}$,
   • the second aromatic ring from coupling.

   Therefore, among the given options, the correct structure is the one corresponding to the azo dye formed from diazotised sulphanilic acid.

4. Matching with the options

   The stored correct option is C, and this matches the expected azo dye structure from sulphanilic acid diazotisation and coupling.

Final Answer

$\boxed{\text{C}}$