A white crystalline solid (A) on boiling with caustic soda solution gave a gas (B) which when passed through an alkaline solution of potassium mercuric iodide gave a brown ppt. The substance (A) on heating gave a gas (C) which rekindled a glowing splinter but did not give brown fumes with nitric oxide. The gases (B), (C) and the substance (A) respectively are
(a) H2S, NO2, NaCl
(b) NH3, N2O, NH4NO3
(c) HCl, NO, NH4Cl
(d) CO2, SO2, Na2SO3
