Question

Why is helium inert, whereas hydrogen can be both reduced and oxidized?

Answer 1

Well, because hydrogen and helium, can possess up to 2 valence electrons.....but hydrogen can be both reduced and oxidized.

Explanation:

For hydrogen and helium we fill the `1s` shell, which can accommodate only the TWO electrons. Now hydrogen can be reduced to give hydride anions, and can also be oxidized to give a formal `H^+`.

By contrast, helium has a FULL valence shell, i.e. `1s^2`, which makes it extremely difficult to either reduce or oxidize. And hence helium, like the other closed-shell Noble gases, is a very unreactive customer.