Yes, CONTRASTIVE is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, N 1, T 1, R 1, A 1, S 1, T 1, I 1, V 4, E 1.

Is it a valid word?

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

of words so related that one contrasts with the other
strikingly different; tending to contrast
syntactically establishing a relation of contrast between sentences or elements of a sentence