UPSC NDA 2 2019 General Ability Solved Paper

Concept:Soft soap is a potassium-based soap, made using potassium hydroxide (KOH) instead of sodium hydroxide.Explanation:Soap is a salt of fatty acids.Hard soaps are made with sodium hydroxide ($\mathrm{NaOH}$) and are solid.Soft soaps are made with potassium hydroxide ($\mathrm{KOH}$), giving them a lower melting point and a softer, more soluble form.Soft soap lathers easily with soft water because it does not contain high levels of calcium ($\mathrm{Ca}^{2+}$) or magnesium ($\mathrm{Mg}^{2+}$) ions.Potassium-based soaps are more soluble in water than sodium-based soaps.Thus, a sample of "soft soap" contains potassium as the key alkali metal.Caesium is not used in soap because it is rare and expensive.Calcium and magnesium soaps are insoluble (scum) and do not produce lather.Therefore, the active base in soft soap is potassium.Answer:Potassium