JEE Main · 2025 · 02 Apr 2025 · Shift 2 · Compounds Containing Nitrogen

At 273 K nitrous acid diazotises sulphanilic acid to the 4-sulphobenzenediazonium ion, which then couples with 1-naphthylamine (activated towards electrophilic attack para to the amino group) in acetic acid to give the red azo dye $\mathrm{HO}{}_3\mathrm{S}-\mathrm{C}{}_6\mathrm{H}{}_4-\mathrm{N}=\mathrm{N}-\mathrm{C}{}_{10}\mathrm{H}{}_6-\mathrm{NH}{}_2$. Its molecular formula is $\mathrm{C}{}_{16}\mathrm{H}{}_{13}\mathrm{N}{}_3\mathrm{O}{}_3\mathrm{S}$, with molar mass $16\times 12+13+3\times 14+3\times 16+32=327{\text{g mol}}^{-1}$. The mass of 0.1 mol is $0.1\times 327=32.7\text{g}$, that is about 33 g.