Given that the hydroxide ion concentration of a solution is [OH-] = 2.1 × 10-4 M, calculate the pH and state whether the solution is acidic, basic, or neutral.

Calculate pOH = -log(OH^-) = ?

Then pOH + pH = pKw = 14. You know pKw and pOH, solve for pH.
If pH < 7 = acidic
pH = 7 = neutral
pH > 7 = basic
Post your work if you get stuck.