Các phân nhóm nào trong bảng hệ thống tuần hoàn có tổng spin trong nguyên tử bằng không?

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.

You would do 1500/4 and the answer is 375