The second ionisation enthalpies of both Cr and Cu are higher than those of the next element. Explain.

Explanation

After the removal of one electron, chromium, acquires half filled `3d^5` electronic configuration and copper acquires completely filled `3d^10` electronic configuration. Therefore, it becomes difficult to remove the second electron from highly stable `3d^5` core in case of Cr and highly stable `3d^10` core in case of Cu. Hence, their second ionisation enthalpies are high.