Among all the isomeric amines of molecular formula C7H9N that contain a benzene ring, the number of isomers that give a positive carbylamine test and…

Benzene-ring isomers of $\mathrm{C_7H_9N}$: benzylamine, $o$-, $m$- and $p$-toluidine, and N-methylaniline. The carbylamine test needs a primary amine, which excludes N-methylaniline (secondary): leaving $4$ primary amines. Coupling with 2-naphthol needs a stable arenediazonium salt at 273 K, which only aromatic primary amines (the three toluidines) provide; benzylamine gives an unstable aliphatic-type diazonium ion that decomposes to benzyl alcohol and $\mathrm{N_2}$. Count $=3$.