Final answer:
The solution that reacts with crushed eggshells to produce carbon dioxide gas, causing limewater to turn milky, must be an acid; hydrochloric acid (HCl) or sulfuric acid (H2SO4) could fulfill this role. Sodium hydroxide (NaOH) is a base and CO2 is not a solution.
Step-by-step explanation:
In the reaction, crushed eggshells which are primarily composed of calcium carbonate (CaCO3), will react with an acid to produce carbon dioxide (CO2) gas. When this gas comes into contact with limewater, a solution of calcium hydroxide (Ca(OH)2), it reacts to form calcium carbonate (CaCO3) which is insoluble in water and precipitates out, causing the limewater to turn milky. The equation for this reaction is CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l).
The solution that reacts with the crushed eggshells to give off carbon dioxide gas, therefore, must be an acid. The options given are hydrochloric acid (HCl), sulfuric acid (H2SO4), and sodium hydroxide (NaOH), which is a base and hence cannot produce carbon dioxide when reacted with a carbonate. Therefore, the correct solutions that could contain the acid reacting with the eggshells to release carbon dioxide can be either hydrochloric acid (HCl) or sulfuric acid (H2SO4). However, based on the information provided, the specific acid used in the experiment is not clearly identified, hence options a (HCl) and b (H2SO4) would both be acceptable answers.