Why neon (Ne) is stable (unreactive), but oxygen (O) is unstable (reactive).?

Neon is the tenth element of the periodic table and the second of the noble gases. The element is incredibly non-reactive because of its electron configuration. It has a "happy" electron orbital that is filled with eight electrons.

Oxygen's high reactivity is due to its biradical electron configuration. As shown in a molecular orbital drawing of O2, the two unpaired electrons make the molecule highly susceptible to bond formation. Oxygen has two allotropes (dioxygen, O2, and ozone, O3), both excellent oxidizing agents (Table P2).

Explanation:

they are all solids.