Yes, SOLUTION is a Scrabble word!

Letter values in Scrabble US: S 1, O 1, L 1, U 1, T 1, I 1, O 1, N 1.

Is it a valid word?

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

a homogeneous mixture of two or more substances; frequently (but not necessarily) a liquid solution
a statement that solves a problem or explains how to solve the problem
a method for solving a problem
the set of values that give a true statement when substituted into an equation
the successful action of solving a problem