nMg = 4.8/24 = 0.2 (mol)
Mg + 2HCl => MgCl2 + H2
0.2.................................0.2
CuO + H2 -to-> Cu + H2O
...........0.2..........0.2
mCu = 0.2*64 = 12.8 (g)
a) PTHH: Mg + 2HCl -> MgCl2 + H2
0,2____________0,4___0,2___0,2(mol)
CuO + H2 -to-> Cu + H2O
0,2___0,2____0,2(mol)
b) =>mCu=0,2.64=12,8(g)