Epsom salt, a common hydrate, has the formula shown below. If I measure out 80 g of epsom salt to add to my foot soak, what mass of the epsom salt is H2O? Please show work!!

MgSO4 x 7H2O

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.