2KMnO4+5H2S+3H2SO4=5S+K2SO4+2MnSO4+8H2O
Mn(+7) +5e= Mn(+2) -2-в-ние; ок-ль
S(-2) -2e=S(0) -5-ок-ние;в-ль
2Mn(+7) + 5S(-2) = 2Mn(+2) + 5S(0)
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