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