Reasons why bleaching powder has deteriorated in the air for a long time
The main component of the bleaching powder is calcium hypochlorite. Calcium hypochlorite reacts with CO2 and water vapor in the air to form hypochlorous acid and calcium carbonate (this reaction is actually the reaction of the bleaching powder). If it is not used, it will be light. The solution (which reacts in the dark for a long time) produces oxygen and hydrogen chloride gas (or hydrochloric acid), so it fails.