WAEC Chemistry 2023 Paper

Concept:The density of a gas is directly related to its molar mass. Lower molar mass means lower density than air.Explanation:Air has an approximate average molar mass of $29\ \text{g mol}^{-1}$.Nitrogen, $\mathrm{N_2}$, has a molar mass of $28\ \text{g mol}^{-1}$, which is less than that of air.Chlorine, $\mathrm{Cl_2}$, has a molar mass of about $71\ \text{g mol}^{-1}$.Carbon(IV) oxide, $\mathrm{CO_2}$, has a molar mass of $44\ \text{g mol}^{-1}$.Oxygen, $\mathrm{O_2}$, has a molar mass of $32\ \text{g mol}^{-1}$.Since only nitrogen has a molar mass lower than the average molar mass of air, it is the gas that is less dense than air.Answer:A. nitrogen