Give the oxidation state,$d$-orbital occupation,and coordination number of the central metal ion in the following complexes:
$(i)$ $K_{3}[Co(C_{2}O_{4})_{3}]$
$(ii)$ $cis-[Cr(en)_{2}Cl_{2}]Cl$
$(iii)$ $(NH_{4})_{2}[CoF_{4}]$
$(iv)$ $[Mn(H_{2}O)_{6}]SO_{4}$

(N/A) $(i)$ $K_{3}[Co(C_{2}O_{4})_{3}]$: Central metal is $Co$. Coordination number is $6$. Oxidation state: $x + 3(-2) = -3 \implies x = +3$. $Co^{3+}$ $(d^{6})$ is $t_{2g}^{6} e_{g}^{0}$.
$(ii)$ $cis-[Cr(en)_{2}Cl_{2}]Cl$: Central metal is $Cr$. Coordination number is $6$. Oxidation state: $x + 2(0) + 2(-1) = +1 \implies x = +3$. $Cr^{3+}$ $(d^{3})$ is $t_{2g}^{3} e_{g}^{0}$.
$(iii)$ $(NH_{4})_{2}[CoF_{4}]$: Central metal is $Co$. Coordination number is $4$. Oxidation state: $x + 4(-1) = -2 \implies x = +2$. $Co^{2+}$ $(d^{7})$ is $t_{2g}^{5} e_{g}^{2}$.
$(iv)$ $[Mn(H_{2}O)_{6}]SO_{4}$: Central metal is $Mn$. Coordination number is $6$. Oxidation state: $x + 6(0) = +2 \implies x = +2$. $Mn^{2+}$ $(d^{5})$ is $t_{2g}^{3} e_{g}^{2}$.