\(n_{Fe_3O_4}=\dfrac{4.64}{232}=0.2\left(mol\right)\)
\(Fe_3O_4+4H_2SO_4\rightarrow FeSO_4+Fe_2\left(SO_4\right)_3+4H_2O\)
\(0.2...............0.8.............0.2...........0.2\)
\(C_{M_{H_2SO_4}}=\dfrac{0.8}{0.2}=4\left(M\right)\)
\(C_{M_{FeSO_4}}=C_{M_{Fe_2\left(SO_4\right)_3}}=\dfrac{0.2}{0.2}=1\left(M\right)\)