Write down the number of $3d$ electrons in each of the following ions:
$Ti^{2+}, V^{2+}, Cr^{3+}, Mn^{2+}, Fe^{2+}, Fe^{3+}, Co^{2+}, Ni^{2+}$ and $Cu^{2+}$
Indicate how you would expect the five $3d$ orbitals to be occupied for these hydrated ions (octahedral).

(N/A) The electronic configuration of the metal ions is determined by removing electrons from the $4s$ orbital first,followed by the $3d$ orbital. In an octahedral field,the $d$-orbitals split into $t_{2g}$ and $e_g$ sets. The filling follows Hund's rule and the Aufbau principle.

Metal ion	Number of $3d$ electrons	Filling of $d$-orbitals
$Ti^{2+}$	$2$	$t_{2g}^2 e_g^0$
$V^{2+}$	$3$	$t_{2g}^3 e_g^0$
$Cr^{3+}$	$3$	$t_{2g}^3 e_g^0$
$Mn^{2+}$	$5$	$t_{2g}^3 e_g^2$
$Fe^{2+}$	$6$	$t_{2g}^4 e_g^2$
$Fe^{3+}$	$5$	$t_{2g}^3 e_g^2$
$Co^{2+}$	$7$	$t_{2g}^5 e_g^2$
$Ni^{2+}$	$8$	$t_{2g}^6 e_g^2$
$Cu^{2+}$	$9$	$t_{2g}^6 e_g^3$