Among the following the incorrect statement is/are 

The most common oxidation state of first row transition metals is +2 which achieves after losing two electrons from 4s. ${\mathrm{Cu}}^{2+}$ has a more charge density and forms stronger bonds than ${\mathrm{Cu}}^{+}.$ The electrode potential of Zn is highly negative because of filled 3d orbitals and this high negative potential value indicates the tendency to loose electrons easily.

Valence electronic configuration of Cr and Mn is $3{\mathrm{d}}^{5}4{\mathrm{s}}^1$ and $3{\mathrm{d}}^{5}4{\mathrm{s}}^2$ respectively. They have maximum number of unpaired electrons, hence shows maximum number of oxidation states.