Yes, REDOXES is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, D 2, O 1, X 8, E 1, S 1.

Is it a valid word?

REDOXES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a reversible chemical reaction in which one reaction is an oxidation and the reverse is a reduction

Also: oxidation-reduction.

Not playable in Scrabble US: OXIDOREDUCTION.