\(Fe+2HCl-->FeCl2+H2\)
\(ZnO+2HCl--.ZnCl2+H2O\)
\(nH2=\frac{2,24}{22,4}=0,1\left(mol\right)\)
\(n_{Fe}=n_{H2}=0,1\left(mol\right)\)
\(m_{Fe}=0,1.56=5,6\left(g\right)\)
\(m_{ZnO}=20-5,6=14,4\left(g\right)\)
\(\%m_{ZnO}=\frac{14,4}{20}.100\%=72\%\)