Gọi x, y là số mol $Zn^{2+}$, $Fe^{3+}$
$n_{OH^-(1)}=n_{NaOH}=0,5.1,4=0,7(mol)$
$Zn^{2+}+2OH^-\to Zn(OH)_2$
$Fe^{3+}+3OH^-\to Fe(OH)_3$
$\Rightarrow 2x+3y=0,7$ (1)
$n_{OH^-(2)}=n_{KOH}=0,2.2=0,4(mol)$
$Zn(OH)_2+2OH^-\to ZnO_2^{2-}+2H_2O$
$\Rightarrow 2x=0,4$ (2)
(1)(2)$\Rightarrow x=0,2; y=0,1$
$n_{ZnSO_4}=x=0,2(mol)\Rightarrow C_{M_{ZnSO_4}}=2M$
$n_{Fe_2(SO_4)_3}=0,5y=0,05(mol)\Rightarrow C_{M_{Fe_2(SO_4)_3}}=0,5M$