Element or compound?
H2O

A.

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.

; lc

Answerrestate the main idea,essay or thesis, summarize the three subpoints of your essay, leave the reader with an interesting final impression;