It's answer 1 (500
Each mole of calcium hydroxide yields 1 mole of calcium carbonate on reaction with carbon dioxide.
50 ml of 0.5M calcium hydroxide solution contains (50/1000) . 0.5 = 0.025 mol
For every mole of calcium carbonate on you need 2 moles of hydrochloric acid, so if you had 0.025 mol of calcium carbonate, you would have used 0.050 mol of hydrochloric acid.
The volume is therefore
(Molarity or normality? In this question it's irrelevant as hydrochloric acid is monoprotic). The atomic mass of calcium is a red herring as well!