suppose an element is in the d-block and period 6 of the periodic table. what is the highest quantum level (n) of its d-orbitals in a ground state atom?

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.