3.
MNH4Cl= se aduna masele atomice ale atomilor componenti
MNH4Cl=14 +4 +35,5=53,5------->1mol=53,5 g
MAl(OH)3 =27 +3.16 +3=78-------1mol=78g
4.
2Ca + O2= 2CaO
CuCO3 =CuO + CO2
Zn +2 HCl =ZnCl2 +H2
AgNO3 +KCl =AgCl + KNO3
