The number of unpaired electrons in $Zn^{2+}$ is

Bullet-proof steel alloy is prepared by using

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

Assertion : Cuprous ion $(Cu^+)$ has unpaired electrons while cupric ion $(Cu^{2+})$ does not.
Reason : Cuprous ion $(Cu^+)$ is colourless whereas cupric ion $(Cu^{2+})$ is blue in the aqueous solution.

$Zn$,$Cd$,and $Hg$ show the properties of

Which one of the following ions is the most stable in aqueous solution?
(At. No. $Ti = 22, V = 23, Cr = 24, Mn = 25$)