Question

1)H2-> H2O-> O2
2) Ca-> CaO-> CaCl2
3) H2-> H2S-> H2SO4

Answer 1

2H2+O2=2H2O
2Ca+O2=2CaO
CaO+2HCl=CaCl2+H2O
H2+S=H2S
H2S+2O2=H2SO4