Answer:
8
Step-by-step explanation:
The element must have a complete octet in order to be unreactive.
Such an unreactive element must be a noble gas/ inert gas/ or group O element.
Most elements on the periodic table try to mimic them.
This configuration makes the group O elements unique and unreactive.
What drives reactively is ability of an atom to lose or gain electron in order to achieve a stable configuration such as that of group O elements.