9. [03.02]
Which of the following pair of elements could possibly be in the same group? (1 point)
X has a 1+ ion; Y has a 1-ion.
O X has an atomic number 15; Y forms a 3-ion.
OX tends to form a 2+ ion; Y tends to gain two electrons.
X will tend to gain one electron; Y has eight electrons in the outer orbit.