Step 1: What are compressed gas propellants?
Aerosol products use propellants to expel the product from the container. Propellants can be liquefied gases or compressed gases.
Step 2: Compressed gas propellants vs liquefied gases.
Chlorofluorocarbons (CFCs), dimethyl ether, and propane are liquefied gas propellants that exist as liquids under pressure. Compressed gas propellants remain as gases and simply push the product out.
Step 3: Why nitrogen is used.
Nitrogen (N2) is chemically inert, non-flammable, non-toxic, and odourless. It does not condense to a liquid at normal aerosol container pressures. These properties make it ideal as a compressed gas propellant in food, pharmaceutical, and cosmetic aerosols.
Step 4: Evaluate distractors.
Chlorofluorocarbons are liquefied gas propellants now banned due to ozone depletion (Montreal Protocol). Dimethyl ether and propane are also liquefied gas propellants and are flammable, making them less safe and not classified as compressed gas propellants.
Step 5: Confirm.
Nitrogen is the most common compressed gas propellant used in pharmaceutical aerosols because it is inert and remains in the gas phase.
Answer: Option (1) — Nitrogen