H2CO3 = CO2 + H2O (1 + 1+ 1 = 3)
N2O5 + H2O = 2HNO3 ( 1 +1+2 = 4)
2Al + 6HCl = 2ALCl3 + 3H2 (2 + 6 + 2 + 3 = 13)
NaCl + AgNO3 = AgCl + NaNO3 (1 + 1+ 1+ 1 =4)
2Al + 3Cl2 = 2AlCl3 (2 + 3 +2 = 7)
SO3 + H2O = H2SO4 (1 + 1+ 1 = 3)
2HCl + MgO = MgCl2 + H2O ( 2+ 1 + 1 + 1= 5)
CaCO3 = CaO + CO2 ( 1+ 1+ 1=3)