The method to separate each component from the mixture is given below:
(i) Hand picking: It is used to separate iron nails from the mixture.
(ii) Decantation: The mixture is allowed to stand for some time. The clear liquid is poured to another container to separate oil from the mixture.
(iii) Evaporation: The remaining liquid is allowed to evaporate till residue is obtained. This residue is salt.

A mixture of salt, sand, oil and water can be separated by following steps:
Step I : First of all, the clear liquid is poured into another container by the process of decantation. By this process, oil is separated from the mixture.
Step II : Now filter the mixture by using filter paper, funnel and container by the process of filtration. By this process, sand is separated from the mixture 

Step III : Finally, the remaining liquid evaporates till the residue in obtained by the process of evaporation. By this process, salt is separated from the mixture.

(a) This is done as follows:
(i) Some water is added to the mixture of sand and salt in a beaker and stirred. Salt dissolves in water to form salt solution, whereas sand remains undissolved. It is then filtered.
(ii) On filtering, sand is obtained as a residue on the filter paper and salt solution is obtained as a filtrate. (iii) The filtrate is evaporated and pure salt is left behind.
(b) The mixture of sand and salt has been separated into its components, i.e sand and salt by doing two methods.
(i) Filtration
(ii) Evaporation
(c) Rohit is knowledgeable and intelligent boy.

(i) happy
(ii) sun
(iii) threshed
(iv) winnowed
(v) handpicked
(vi) sieved
They got a good price as they used appropriate methods of separation to get good quality of flour (atta).

(a) They will mix salt with water within a certain amount to make salt solution. Hence, Sarika will make a better salt solution.
(b) Saturation is the point at which a solution of a substance can dissolve no more of that substance and additional amount of that substance will appear as a precipitate, Mohan's solution would be saturated because in Mohan's case, some salt would remain undissolved and settled at the bottom of the glass.