Question 2
Argon has the electron configuration 2, 8, 8 and forms almost no compounds. Why is it so unreactive?
The right answer is the one marked above.
Its valence shell already holds eight electrons. Eight is a stable arrangement, so argon has nothing to gain by losing, gaining or sharing electrons.
Argon does contain neutrons, and its mass has nothing to do with its reactivity — the far heavier metals react readily. An atom with an empty outer shell would be extremely reactive, not unreactive.