Yes, REFLEXIVITY is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, F 4, L 1, E 1, X 8, I 1, V 4, I 1, T 1, Y 4.

Is it a valid word?

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

the coreferential relation between a reflexive pronoun and its antecedent
(logic and mathematics) a relation such that it holds between an element and itself