How would the size of the xenon atom compare to that of the neon atom?
Well, have you got a Periodic Table in front of you?
You should have one, because you are doing your chemistry homework.
And given a Periodic Table, you must remember this mantra:
from left to right as we face the Table. This is a consequence of increased nuclear charge. But..........
Once a shell is filled, the shell shields the nuclear charge fairly effectively, and the next valence shell is removed to a greater radius.
We have got second Period neon, a Group 18 inert gas, VERSUS fifth Period xenon, another inert gas. The xenon atom, will be vastly greater in size than neon.
As chemists, as physical scientists, however, we should put some numbers on our explanation, i.e. we rely on numerical data.
This site quotes the atomic radius of neon as