WAEC Chemistry 2022 Paper

Concept:An alkaline gas is a gas that produces a basic solution with a pH greater than $7$ when dissolved in water.Explanation:When ammonia, $\mathrm{NH}_3$, dissolves in water, it forms ammonium hydroxide: $\mathrm{NH}_3 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{NH}_4^+ + \mathrm{OH}^-$.This solution contains hydroxide ions, $\mathrm{OH}^-$, so it is alkaline and has a pH greater than $7$.In contrast, $\mathrm{NO}_2$ and $\mathrm{CO}_2$ dissolve to form acidic solutions.$\mathrm{N}_2\mathrm{O}$ is essentially neutral and does not show alkaline properties.Hence, ammonia is the most common alkaline gas among the given options.Answer:C. $\mathrm{NH}_3$