What is the concentration of hydroxide ion in household ammonia, an aqueous solution of nh3 that has a ph of 11.50?

 The  concentration  of  hydroxide  ion    in   household  of  ammonia  that  has  a  ph  of  11.50  is  calculated  as follows
as  we   well  know    Ph  +POh=  14

POh  is  therefore=14  -11.50= 2.5

POh  is  calculated  as  follows

POh=  -log(-OH)= 2.5
-OH  concentration  is  therefore   =  10^-2.5 =3.162  x10^-3

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.