Which of the following equations is not balanced?
O 2NaHCO₃ + H₂SO₄ -> Na₂SO₄ + 2H₂O + CO₂
O 2NO + O₂ -> 2NO₂
O Cu + 2AgNO₃ -> Cu(NO₃)₂ + 2Ag
O 2Mg + O₂ -> 2MgO
O CaCO₃ -> CaO + CO₂