Benzene diazonium chloride when reacts with hypophosphorus acid produces

when diazonium salt is treated with H₃PO₂ followed by hydrolysis, diazonium group is replaced by- H resulting to the formation of hydrocarbon. Thus, A, must be ${\mathrm{H}}_3{\mathrm{PO}}_2/{\mathrm{H}}_2\mathrm{O}$.