Question

Calculate the amount of NaOH in this solution

5.00mL of 12.0 NaOH is diluted with water to make 24 mL of 2.50 NaOH solution

Answer 1

Ignore the 24 mL and 2.50 M. What you have is what you originally put in. That is 5.00mL x 12.0 M (you didn't put units but I'm guessing M). So mols = M x L and grams = mols x molar mass or about 2.4 grams of NaOH.