a) 2K + 2HCl--->2KCl+H2
2K +2H+ +2Cl- --->2K+ +2Cl- +H2
2K +2H+ --->2K+ +H2
K2O + 2HNO3--->2KNO3+H2O
K2O +2H+ +2NO3- --->2K+ +2NO3- +H2O
K2O +2H+ --->2K+ +H2O
2KOH + H2SO4--->K2SO4+2H2O
2K+ +2OH- +2H+ +SO4 2- --->2K+ +SO4 2- +2H2O
2OH- +2H+ --->2H2O
2K+S ->K2S
2K +S --->2K+ +S2-
b) Mg + H2SO3--->MgSO3+H2
Mg +2H+ +SO3 2- --->Mg2+ +SO3 2- +H2
Mg +2H+ --->Mg2+ +H2
MgO + H2S--->MgS+H2O
MgO +2H+ +S2- --->Mg2+ +S2- +H2O
MgO +2H+ --->Mg2+ +H2O
Mg(OH)2 + 2HNO3--->Mg(NO3)2+2H2O
Mg2+ +2OH- +2H+ +2NO3- --->Mg2+ +2NO3- +2H2O
2OH- +2H+ --->2H2O
Mg + Cl2 ->MgCl2
Mg +Cl2 --->Mg2+ +2Cl-
c) 2NaOH + SO2--->Na2SO3+H2O
2Na+ +2OH- +SO2 --->2Na+ +SO3 2- +H2O
2OH- +SO2 --->SO3 2- +H2O
Ca(OH)2 + CO2--->CaCO3+H2O
Ca2+ +2OH- +CO2 --->Ca2+ +CO3 2- +H2O
2OH- +CO2 --->CO3 2- +H2O
CuO + N2O5--->Cu(NO3)2
CuO +N2O5 --->Cu2+ +2NO3-
d) BaO + SO3--->BaSO4
BaO +SO3 --->Ba2+ +SO4 2-
6ZnO + P4O10-->2Zn3(PO4)2
6ZnO +P4O10 --->6Zn2+ +4 PO4 3-