Question

Which pairs of elements have the same number of valence electrons?

Answer 1

for the representative elements usually the ones that are in the same group have the same number of valence electrons. In the transition elements it is a little more complicated I will said they all have 2 valence electrons, if you consider the electrons in the outermost shell only, but different authors explain in different way.
http://www.wikihow.com/Find-Valence-Electrons