Which one of the following sets of quantum numbers could be those of the distinguishing (last) electron of Mo?

Q. Which one of the following sets of quantum numbers could be those of the distinguishing (last) electron of Mo?

A.            n = 4, l = 0, ml = 0, ms = +1/2

B.            n = 5, l = 1, ml = 9, ms = -1/2

C.            n = 4, l = 2, ml = -1, ms = +1/2

D.            n = 5, l = 2, ml = +2, ms = -1/2

Answer: n = 4, l = 2, ml = -1, ms = +1/2