Answer:
This question is incomplete
Step-by-step explanation:
This question is incomplete. However, the element X with the atomic number of 18 is Argon (Ar) while the next element (element Y) in the periodic table, with atomic number 19, is potassium (K).
Element X is found in the group zero (also called group 18 and elements found therewith are referred to as noble gases) of the periodic table while element Y is found in group 1 (elements found here are referred to as alkali metals).
Element X has a completely filled outermost shell while element Y has one electron in its outermost shell.
Element X is a metal while element Y is a nonmetal.