Rounding to significant figures? I'm not sure about how many significant figures the result should be rounded
(7.14 e4) + (2.8 e2) = 7.1689 e4
This shoul be rounded to 7.17 ? 7.169 ? Not rounding?
Or any other option?

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.