What is the oxidation number of Cl in KCl ​

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.

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

It would be c. risk.

The ground state electron configuration of a phosphorous atom has  three unpaired electrons. they're in the 3p sublevel. the electron configuration is: , for a total of  15 electrons.