Answer:
Their electronic configuration.
Explanation:
Atomic propreties can be undestood upon analisis of its electronic configuration, because the way that electrons fill up the atomic orbitals will determine its reactivity.
So, if element X when combined with Y or Z givez XY or XZ it means that Y and Z must have the same electronic configuration.
The periodic table is made in a way that atoms with the same electronic configuration are at the same group, so Y and Z must be at the same group as well.
