Which of the following amines, when diazotised with $\mathrm{NaNO}{}_2$ / dil. $\mathrm{HCl}$ at 273-278 K and then treated with $\mathrm{H}{}_3\mathrm{PO}{}_2$, give toluene?

The methyl-substituted primary aromatic amines (2-, 3- and 4-methylaniline) give the methylbenzenediazonium salt, and $\mathrm{H}{}_3\mathrm{PO}{}_2$ replaces $\mathrm{N}{}_2{}^{+}$ by H to give toluene. Benzylamine is aliphatic, so it loses nitrogen as the alcohol, and N-methylaniline is secondary and gives an N-nitroso compound.