Ethyne can be prepared in the laboratory by the action of water on

Explanation

Calcium carbide reacts vigorously with water to give ethyne and calcium hydroxide, which was once used in carbide lamps and is still the classic laboratory preparation. Calcium carbonate with acid would give carbon dioxide instead, which is the tempting confusion between the carbide and the carbonate. The ethyne produced this way smells unpleasant because of phosphine impurities.