How much NaOH (g) would you need to dissolve in water in order to prepare 2.75 L of a NaOH solution in which [OH-]= 0.50 M?

Answer 1

(OH^-) = 0.50M; therefore, NaOH = 0.5M.
How many mols do you need? That's M x L = 0.5M x 2.75L = ?
Then mols = grams/molar mass. You know molar mass and mols, solve for grams.

Answer 2

54.996 or 55.0 g NaOH