JEE Main · 2021 · 22 Jul 2021 · Shift 2 · General Principles and Processes of Isolation of Metals

Sulphide ion is large and highly polarisable, a soft base, and is bound most firmly by soft cations of low charge density. Lead and silver give such cations and occur naturally as galena, $\mathrm{PbS}$, and argentite, $\mathrm{A}{\mathrm{g}}_2\mathrm{S}$. Aluminium and magnesium give small, hard cations of high charge density that bind the hard oxide, carbonate and silicate bases instead, which is why they are mined as bauxite and as carbonates and silicates. Sulphide ores are therefore common for lead and silver.