Account for the fact that second ionization energies of both Cr and Cu are higher than those of the next element.

Explanation

This is because the outer electronic configuration of `Cr^(o+)` is `3d^(5)` (half filled) and that of `Cu^(o+)` is `3d^(10)` (completely filled). The second ionisation of Cr means the removal of one electron from the highly stable `3d^5` core. Similarly, the second ionisation of Cu needs removal of one electron from highly stable `3d^(10)` core.