A gas evolved by adding acid to a carbonate turns lime water milky. Which gas is it?
Answer and explanation
Correct answer: Carbon dioxide
The governing concept is the acid–carbonate reaction and the limewater test. An acid reacts with a carbonate to form a salt, water, and carbon dioxide; for example, CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. When CO₂ is passed through limewater, it forms insoluble calcium carbonate, CaCO₃, which makes the solution milky. Hydrogen, nitrogen, and ammonia do not give this characteristic test. Therefore, option A is correct.
Frequently asked questions
What is the correct answer to this question?
Carbon dioxide
Why is this the correct answer?
The governing concept is the acid–carbonate reaction and the limewater test. An acid reacts with a carbonate to form a salt, water, and carbon dioxide; for example, CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. When CO₂ is passed through limewater, it forms insoluble calcium carbonate, CaCO₃, which makes the solution milky. Hydrogen, nitrogen, and ammonia do not give this characteristic test. Therefore, option A is correct.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
