Yes, LIQUIDNESS is a Scrabble word!

Letter values in Scrabble US: L 1, I 1, Q 10, U 1, I 1, D 2, N 1, E 1, S 1, S 1.

Is it a valid word?

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

the state in which a substance exhibits a characteristic readiness to flow with little or no tendency to disperse and relatively high incompressibility
the property of flowing easily

Also: liquid state.