Explanation:

- Calcium hypochlorite is commonly used for water treatment and as a bleaching agent.

- Correct Answer: Option 2: Bleaching powder is another name for calcium hypochlorite.

- Option 1: Bordex mixture is not related to calcium hypochlorite; it's actually Bordeaux mixture, a fungicide containing copper sulfate and lime.

- Option 3: Laughing gas refers to nitrous oxide, a different compound used for anesthesia.

- Option 4: Gunpowder is a mix of sulfur, charcoal, and potassium nitrate, known for its use in firearms, rather than for its chemical similarities to calcium hypochlorite.