Second ionisation energy is maximum for :

$\begin{array}{l}\mathrm{Zn}\stackrel{{\mathrm{IE}}_1}{⟶}3{\mathrm{d}}^{10}4{\mathrm{s}}^1\stackrel{{\mathrm{IE}}_2}{⟶}\\ \mathrm{Sc}\stackrel{{\mathrm{IE}}_1}{⟶}3{\mathrm{d}}^{0}4{\mathrm{s}}^2\stackrel{{\mathrm{IE}}_2}{⟶}\\ \mathrm{Cu}\stackrel{{\mathrm{IE}}_1}{⟶}3{\mathrm{d}}^{5}4{\mathrm{s}}^0\stackrel{{\mathrm{IE}}_2}{⟶}\\ \mathrm{Ni}\stackrel{{\mathrm{IE}}_1}{⟶}3{\mathrm{d}}^{7}4{\mathrm{s}}^1\stackrel{{\mathrm{IE}}_2}{⟶}\end{array}$

Maximum IE₂ is of Cu, half filled configuration and more Z_eff (3d⁵ > 4s²).