Yes, RESISTANCES is a Scrabble word!

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

Is it a valid word?

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

the action of opposing something that you disapprove or disagree with
any mechanical force that tends to retard or oppose motion
a material's opposition to the flow of electric current; measured in ohms
the military action of resisting the enemy's advance
(medicine) the condition in which an organism can resist disease
the capacity of an organism to defend itself against harmful environmental agents
a secret group organized to overthrow a government or occupation force
the degree of unresponsiveness of a disease-causing microorganism to antibiotics or other drugs (as in penicillin-resistant bacteria)
(psychiatry) an unwillingness to bring repressed feelings into conscious awareness
an electrical device that resists the flow of electrical current
group action in opposition to those in power

Also: electric resistance, electrical resistance, ohmic resistance.