Determine the element of lowest atomic number that contains a complete d subshell in the ground state.?

1s2 2s2 2p6 3s2 3p6 4s2 3d10

Total number of electrons = 30

Element with atomic number of 30 = zinc
It is element 29 Copper: [Ar] 3d^10 4s^1 that it is not [Ar] 3d^9 4s^2 is attributed to the”extra stability of a completely filled d shell.” It is also now thought that 3d should come before 4s in energy. The higher energy 4s AO is occupied first because it minimizes the electron-electron repulsions with core electrons.

http://en.wikipedia.org/wiki/Copper RH panel agrees with the configuration given

I am not sure how you would determine the configuration; Cu is an exception to the rule.
Thanks!