What is the major element per mass in naoh? a. oxygen b. all elements contribute the same mass. c. hydrogen d. sodium?

The mass of Na in NaOH is 23 g, For H it is 1 and for O it is 16. The major element based on the mass is Sodium/Na, so D.

The answer to that would be magnesium

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.