Excess of carbon dioxide is passed through 50 \(\mathrm{mL}\) of \(0.5 \mathrm{M}\) calcium hydroxide solution. After the completion of the reaction, the solution was evaporated to dryness. The solid calcium carbonate was completely neutralised with \(0.1 \mathrm{~N}\) hydrochloric acid. The volume of hydrochloric acid required is (Atomic mass of calcium \(=40\) )

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.