Following is a confirmatory test for aromatic primary amines. Identify reagent (A) and (B)

Aniline reacts with ${\mathrm{NaNO}}_2 \text{and} \mathrm{HCl}$ to form benzene diazonium chloride which further reacts with $\mathrm{\beta }$ napthol to give a scarlet red dye.

The reaction is as follows,

Hence here,