Which statement about chlorine gas is true?

• A. heavier than air
• B. harmless to humans
• C. highly flammable
• D. lighter than air

Answer: (A)

Chlorine gas is heavier than air. Its density at standard conditions is about 3.2 g/L, while air is around 1.2 g/L, so chlorine tends to sink and accumulate in low-lying areas, basements, or pits if released. This property is important for safety in facilities where chlorine is used or stored, because leaks can create hazardous concentrations in confined spaces.

Chlorine gas is not harmless to humans: it is a toxic irritant that can cause coughing, watering of the eyes, throat irritation, chest tightness, and at higher exposures can lead to serious respiratory injury or death. It is also not highly flammable; it does not burn on its own, though it can react with certain substances and fuels. It is not lighter than air. So the statement that chlorine gas is heavier than air is the correct one.