Why is the 2nd ionisation energy of zinc lower than that of copper? ?

Question

supposed to involve 5 consecutive d-blocks elements, iron, cobalt, nickel, copper, and zinc.

Answer 1

Zn is lower than Cu because it has 2 electrons in it's outer orbit wheras copper only has one.  to get to the second ionzation in copper you must remove an electron from a lower orbital requiring more energy.  

The 2nd Ionisation energy is just what is the 2nd easiest electron to remove from the atom.  It just happens to be this electron in this case because the other electrons are in lower energy states, they prefer to stay in the atom.