Z,Mg= 12--->-1atom are 12e
1mol at are 12x6,023x10²³ e
4mol.................4x12x6,023x10²³ e
Z,Ca= 20----> 1atom are 20e
1mol at. are.....20x6,023x10²e
x.......................4x12x6,023x10²³e
x= 48/20 mol Ca
m= nxM=> m,Ca= 2,4molx40g/mol= calculeaza !!!!