ANS:C - both (a) and (b).

Substances from Non-Volatile Impurities: In this scenario, steam distillation is employed to separate substances that are volatile (i.e., have a tendency to vaporize) from non-volatile impurities (i.e., substances that do not easily vaporize). For example, consider a mixture where a volatile compound, such as an essential oil or a flavoring agent, is contaminated with non-volatile impurities like salts or other solids. By subjecting the mixture to steam distillation, the volatile compound can be selectively vaporized and carried away by the steam, leaving behind the non-volatile impurities in the boiling flask or still. The distillate collected will contain the purified volatile compound, free from the non-volatile impurities.

1. Volatile Impurity from Still Higher Boiling Substances: In this case, steam distillation is used to separate a volatile impurity from a mixture of substances with even higher boiling points. For instance, consider a mixture containing a high boiling substance (e.g., a resin or a polymer) contaminated with a volatile impurity. By employing steam distillation, the volatile impurity can be preferentially vaporized and carried away by the steam, while the higher boiling substance remains in the boiling flask or still. The distillate collected will contain the purified volatile impurity, separated from the higher boiling substances.

In both scenarios, steam distillation takes advantage of the differential boiling points and vapor pressures of the components in the mixture to achieve separation. By introducing steam, which acts as a carrier for the volatile components, the process allows for the selective vaporization and removal of the desired substances while leaving behind the non-volatile impurities or higher boiling substances.