Explanation:

- Option 1: Nitrous oxide

- Commonly known as laughing gas.

- Used as an anesthetic and in whipped cream canisters.

- Not used as a food preservative.

- Option 2: Phosgene

- A toxic gas.

- Known for its use in chemical warfare.

- Not used in food preservation.

- Option 3: Sulphites

- Used as preservatives in foods and beverages.

- Help prevent browning and discoloration.

- Can cause allergic reactions in some people.

- Correct Answer

- Option 4: Chlorine

- Used as a disinfectant.

- Not typically used as a preservative in foods to prevent browning.