Q. Excess of carbon dioxide is passed through 50 ml of 0.5 M calcium hydroxide solution.  After the completion of the reaction, the solution was evaporated to dryness. The solid calcium carbonate was completely neutralised with 0.1 N Hydrochloric acid. The volume of Hydrochloric acid required is? (At. mass of calcium = 40)

1. 200 cm3
2. 300 cm3
3. 400 cm3
4. 500 cm3