Describe the principle involved in each of the following processes: (i) Mond process for refining of nickel (ii) Column chromatography for purification of rare elements

(i) Nickel is combined with carbon monoxide to form a volatile complex which is further decomposed to get back pure nickel.
Ni(s) + 4CO(g) → Ni(CO)₄(g)
Ni(CO)₄(g) → Ni(s) + 4CO(g)
(ii) Column chromatography is the technique used to separate constituent elements from mixtures. This method is largely used to separate rare elements available in less quantity. This chromatography is based on the principle of adsorption of different components of the mixture differently. In column chromatography, there are two phases: mobile phase and stationary phase. The stationary phase is immobilized and immiscible. Usually Al₂O₃ is used as the stationary phase. The mobile phase may be a gas, liquid, or supercritical liquid. The mobile phase is allowed to move through the stationary phase. Then the component that is more strongly adsorbed will take more time to move through the mobile phase, and the component which is loosely adsorbed on the stationary phase will take less time to move. Then the adsorbed components can be separated using suitable solvents.