(a) Mercury and water are separated by using a separating funnel.

Mercury and water are two immiscible liquids having different densities. Thus they are separated by the process of decantation* using separating funnel. Mercury is heavier than water, thus forms the lower layer and is separated from water.

*Decantation: It is a process in which the mixtures are. This separation is done by removing a layer of liquid in which a precipitate has settled.

(b) Potassium chloride and ammonium chloride are separated by sublimation because ammonium chloride sublimes (i.e. changes into vapours) leaving behind the potassium chloride. Sublimation is the process in which solid changes directly into vapours on heating and vapours change into solid on cooling without going in liquid state.

(c) Common salt, water and sand are separated by (i) decantation (or filtration) (ii) evaporation Decantation (or filtration) is used to separate sand from common salt solution in
water. Common salt is soluble in water whereas sand is insoluble in water. Therefore, sand is separated as residue and filtrate is a common salt solution in water.

(ii) Evaporation is used to separate common salt from water. Water evaporates and common salt remains as residue.

(d) Separation of kerosene oil from salt solution is done by using separating funnel to separate kerosene oil followed by evaporation or distillation.
(i) Decantation separates kerosene oil from salt solution in water as these are immiscible and form separate layers.
(ii) Evaporation is used to separate salt from water (as shown above).