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 MnO42- when KMnO4 (violet) is heated.

Thus, (A) = KMnO4
(B) = K2MnO4

(C) = MnO2
(D) = MnCl2

KMnO4 K2MnO4 +  MnO2 + O2
A                       B           C

2MnO4 + 4KOH + O2 → 2K2MnO4 + 2H2O

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

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