A solution reacts with crushed eggshells to give a gas that turns lime-water milky. The solution contains a) NaCl (b) HCl (c) LiCl (d) KCl

The answer is (b) HCl.

Eggshells are made by calcium carbonate (CaCO₃), which in reaction with HCl, liberates CO₂ gas, which turns lime water[Ca(OH)₂] into milky due to formation of milky colour of calcium carbonate(CaCO₃).

CaCO₃(s)​ + 2HCl(aq)​ → CaCl₂(aq) ​+ H₂​O(l) ​+ CO₂(g)​

Ca(OH)₂(aq) + CO₂(aq) → CaCO₃(s) + H₂O(l)