H2S + O2 = S + H2O
K + H2O = KOH + H2
Mg + HCl = MgCl2 + H2

H2S+4O2=S+2H2O

Mg+2HCl=MCl2+H2

2K+2H2O=2KOH+H2

2H2S + O2 --> 2S + 2H2O

2K + 2H2O --> 2KOH + H2↑

Mg + 2HCl --> MgCl2 + H2↑