$\begin{array}{1 1}(A)\;Fe\quad\underrightarrow{Cl_2heat}\quad FeCl_3\quad\underrightarrow{\text{heat,air}}\quad FeCl_2\quad \underrightarrow{Zn}\quad Fe\\(B)\;Fe \quad\underrightarrow{O_2heat}\quad Fe_3O_4\quad\underrightarrow{CO,600^{\large\circ}C}\quad FeO\quad\underrightarrow{CO,700^{\large\circ}C}\quad Fe\\(C)\;Fe \quad\underrightarrow{dilH_2SO_4}\quad FeSO_4 \quad\underrightarrow{H_2SO_4,O_2}\quad Fe(SO_4)_3\quad\underrightarrow{heat} \quad Fe\\(D)\;Fe\quad\underrightarrow{O_2heat}\quad FeO\quad \underrightarrow{dilH_2SO_4}\quad FeSO_4\quad \underrightarrow{heat}\quad Fe\end{array} $
