Question

P+O2
K+O2
O+O
H+H
Mg+H2O

Answer 1

P+O2=P2O5
K+O2=K2O
O+O=O2
H+H=H2
Mg+H2O=MgO + H2

Answer 2

4P+5O2=2P2O5
4K+02=2K2O
O+O=O2
H+H=H2
Mg+2H2O=Mg(OH)2+H2