Q.Which will be adsorbed more readily on the surface of charcoal, and why — $\text{NH}_3$ or $\text{O}_2$?

Adsorption underlies a very wide range of practical applications. Charcoal-based gas masks (used by both British and American forces in World War I) protect against poisonous gases by adsorbing them before they can be inhaled. Activated charcoal is used by Tait and Dewar to create high vacuum in vessels, while alumina and silica gel dry and purify gases such as $\text{CO}_2$, $\text{N}_2$, $\text{Cl}_2$, $\text{O}_2$ and He (silica gel also dries blast-furnace air). Permutit softens hard water by adsorbing $\text{Ca}^{2+}$/$\text{Mg}^{2+}$ via ion exchange ($\text{Na}_2\text{Al}_2\text{Si}_2\text{O}_{12} + \text{CaCl}_2 \rightarrow \text{CaAl}_2\text{Si}_2\text{O}_{12} + 2\text{NaCl}$) and is regenerated with fresh brine. Ion exchange resins demineralise water by passing it through a cation-exchange column (exchanging $\text{Ca}^{2+}$/$\text{Mg}^{2+}$ for $\text{H}^+$) and an anion-exchange column (exchanging dissolved anions for $\text{OH}^-$), the released $\text{H}^+$ and $\text{OH}^-$ then combining to give pure water. Fuller's earth and silica gel refine petroleum and vegetable oils; animal charcoal decolourises sugar made from molasses; chromatography separates a mixture's components by their differing extent of adsorption on an adsorbent, sensitive even to trace quantities. …