(1) $Cu^{2+}(3d^{10})$ is more stable than $Cu(I)$ though $Cu(I)$ has a $3d^{10}$ electronic-configuration
(2) $Cu^{2+}(3d^{10})$ is less stable than $Cu(I)$ because $Cu(I)$ has a $3d^{10}$ electronic-configuration
(3) A 4s sub-shell is filled prior to 3d but on ionization, 4s electrons are removed
(4) A 4s sub-shell is not filled prior to 3d and on ionization, 4s electrons are removed
$\begin{array}{1 1} Cu \\ Zn \\ Sc \\ Mn\end{array}$
