Answer:
Y and Z
Step-by-step explanation:
Since both Y and Z has one valence electron each, they both belong to the same group (group 1) called Alkali metal group. Elements in this group have one valence electron in their outermost shell (e.g, Lithium has 3 proton and it configuration is 2, 1 and the 1 there clearly indicates its group) other examples are sodium, potassium, rubidium and francium. They all have the same properties due to one valence electron they have in common.