Ammonia (NH3) is lighter than air. This is because its molar mass is lower than that of air, which is mostly composed of nitrogen and oxygen. When released into the air, ammonia gas rises due to the buoyancy force exerted by the air around it. In contrast, carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen chloride (HCl) are heavier than air and tend to settle towards the ground when released.