Yes, MENTALITY is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, N 1, T 1, A 1, L 1, I 1, T 1, Y 4.

Is it a valid word?

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

a habitual or characteristic mental attitude that determines how you will interpret and respond to situations
mental ability

Also: mind-set, learning ability, mental capacity.