M(Fe)+m(Cu)=12g
v(Cl2)=5.6l=0.25mol
2Fe+3Cl2=2FeCl3
Cu+Cl2=CuCl2
n(Fe)=x n(Cu)=y
56x+64y=12
n(Cl2)=1.5x+y=0.25
56x+64y=12
1.5x+y=0.25; y=0.25-1.5x
56x+64(0.25-1.5x)=12
56x+16-96x=12
-40x=-4
x=0.1 n(Fe)=0.1mol
y=0.25-1.5*0.1=0.1 n(Cu)=0.1mol
m(Fe)=0.1*56=5.6g
m(Cu)=0.1*64=6.4g
w(Fe)=5.6\(5.6+6.4)=5.6/12=0.467(46.7%)
w(Cu)=1-0.467=0.533(53.3%)