Hydraulic washing seperation method depends upon the difference in the specific gravity of mineral and gangue.
Magnetic separation uses a magneti to physically separate magnetic material from non-magnetic.
Froth floatation is a physical seaparation process of selective wetting of particle with oil to make a foam with air leaving gangue particle down.
But leaching involves the treatment of the ore with a suitable chemical reagent to make the element into a souble compex leaving gangue paticles insoluble.
For example: Extraction of Al from bauxite.
Al2O3(s)+2NaOH(aq)→2Na[Al(OH)4](aq)
Sodium Aluminate is filtered. The filtrate is neutralised by passing CO2 gas.
2Na[Al(OH)4](aq)+CO2(g)→Al2O3.xH2O(s)+2NaHCO3(aq)
The sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to about 1200∘C to get pure Alumina (Al2O3).
Al2O3.xH2O(s)1470K−−−−→Al2O3(s)+xH2O(g). So, a, b and d are physical process of separation while opion c involves chemical treament and not a physical method.
Option c is the right answer