A violet compound of magnese A decomposes on heating to liberate an oxygen and compounds B and C of magnese are formed .compound C reacts with KOH in presence of potassium nitrate to give compound B .On heating compound C with H2So4 and NaCl, chlorine gas is liberated and compound D of magnese along with other product is formed.Identify compound A to D and also explain the reaction involved.

The compound (C) on treating with conc. H2S04 and NaCl gives Cl2 gas, so it is manganese dioxide (MnO₂). It is obtained along with when MnO₄^2- when KMnO₄ (violet) is heated.

Thus, (A) = KMnO₄
(B) = K₂MnO₄

(C) = MnO₂
(D) = MnCl₂

KMnO₄ $\stackrel{∆}{\to }$ K₂MnO₄ +  MnO₂ + O₂
A                       B           C

2MnO₄ + 4KOH + O2 → 2K₂MnO₄ + 2H₂O

MnO₂ + 4NaCl + 4H₂SO₄ → MnCl₂ + 4NaHSO₄ + 2H₂O + Cl₂
                                                  D