Question

Compare the stability of $+2$ oxidation state for the elements of the first transition series.

Answer 1

Oxidations states of first transition metals are shown below:
$\text{Element}$ $\text{Oxidation states}$

$Sc$	$+3$
$Ti$	$+1$	$+2$	$+3$	$+4$
$V$	$+1$	$+2$	$+3$	$+4$	$+5$
$Cr$	$+1$	$+2$	$+3$	$+4$	$+5$	$+6$
$Mn$	$+1$	$+2$	$+3$	$+4$	$+5$	$+6$	$+7$
$Fe$	$+1$	$+2$	$+3$	$+4$	$+5$	$+6$
$Co$	$+1$	$+2$	$+3$	$+4$	$+5$
$Ni$	$+1$	$+2$	$+3$	$+4$
$Cu$	$+1$	$+2$
$Zn$		$+2$

$Sc\left(II\right)$ is virtually unknown, $Ti\left(IV\right)$ is more stable than $Ti\left(II\right)$. As we move from left to right, the stability of higher oxidation states(sum of $s$ and $d$ electrons) increases in the middle and then abruptly the stability of higher oxidation states decreases in the right side and they show lower oxidation states $(+2,+3)$. $Zn$ only shows $+2$ oxidation state. Hence, the stability of $+2$ state increases from left to right in the series.