When air is passed through alkaline pyrogallol and then lime water, the gases left are

Explanation

Air is a mixture of gases. The main components are nitrogen (about 78%), oxygen (about 21%), carbon (IV) oxide (CO₂, about 0.04%), noble gases like argon, neon, and helium (about 1%), and small amounts of water vapor.

Alkaline pyrogallol is a chemical that absorbs oxygen from air. When air is first passed through alkaline pyrogallol, all the oxygen is removed. After this step, the remaining gases are nitrogen, carbon (IV) oxide, and the noble gases.

The air is then passed through lime water, which is calcium hydroxide solution Ca(OH)₂. Lime water absorbs carbon (IV) oxide by reacting with it: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. This removes all the CO₂ from the mixture.

After both treatments, the gases left are nitrogen and the noble gases (mainly argon). Nitrogen is not absorbed by either chemical because it is very unreactive at room temperature. Noble gases are also left because they are inert and do not react with alkaline pyrogallol or lime water.