Ca → CaO → Ca(OH)₂ → Ca(NO₃)₂.
2Ca + O₂ = 2CaO.
CaO + H₂O = Ca(OH)₂.
Ca(OH)₂ + 2HNO₃ = Ca(NO₃)₂ + 2H₂O.
Mg → MgO → MgCl₂ → Mg(OH)₂.
2Mg + O₂ = 2MgO.
MgO + 2HCl = MgCl₂ + H₂↑.
MgCl₂ + 2NaOH = Mg(OH)₂↓ + 2NaCl.
S → SO₂ → H₂SO₃ → K₂SO₃.
S + O₂ = SO₂.
SO₂ + H₂O = H₂SO₃.
H₂SO₃ + 2KOH = K₂SO₃ + 2H₂O.
C → CO₂ → CaCO₃.
C + O₂ = CO₂.
CO₂ + CaO = CaCO₃.