When a brown compound of Mn(A) is treated with HCl, it gives a gas (B) as shown below. MnO2(A)+4HCl→MnCl2+2H2O+Cl2(B) The gas (B) taken in excess reacts with NH3 to give an explosive compound (C) as shown below. 3Cl2(B)+NH3→NCl3(C)+3HCl Therefore, the compounds A,B and C are MnO2,Cl2, and NCl3.