JEE Main · 2020 · 04 Sep 2020 · Shift 1 · General Principles and Processes of Isolation of Metals

All four statements describe standard metallurgical facts. In iron extraction the limestone decomposes, $\mathrm{CaCO}{}_3\to \mathrm{CaO}+\mathrm{CO}{}_2$, and the $\mathrm{CaO}$ formed combines with silica as a flux, $\mathrm{CaO}+\mathrm{SiO}{}_2\to \mathrm{CaSiO}{}_3$. Silver is leached as the anionic cyanide complex $[\mathrm{Ag}(\mathrm{CN}){}_2]{}^{-}$. Nickel is refined by the Mond process, forming volatile $\mathrm{Ni}(\mathrm{CO}){}_4$ that decomposes to give pure nickel. Zirconium and titanium are purified by the van Arkel method, through volatile iodides that break down on a hot filament. Hence all of (a), (b), (c) and (d) are correct.