Identify each technique and its standard use

We match each distillation technique with the most suitable application.

(A) Distillation

Simple distillation is used for:

• separating a liquid from non-volatile impurities, or
• separating two liquids having large difference in boiling points.

Consider chloroform-aniline mixture:

• Boiling point of chloroform $\approx 61^\circ\text{C}$
• Boiling point of aniline $\approx 184^\circ\text{C}$

The boiling point difference is very large, so simple distillation is suitable.

Hence, $A \to IV$

(B) Fractional distillation

Fractional distillation is used for separating liquids with close boiling points, and industrially for separating mixtures into fractions.

Crude oil is separated into different fractions such as petrol, kerosene, diesel, etc. by fractional distillation.

Hence, $B \to III$

(C) Steam distillation

Steam distillation is used for substances that are:

• steam volatile,
• immiscible with water,
• and may decompose at their boiling point.

Aniline-water mixture is a classic example handled by steam distillation because aniline is only slightly soluble in water and is steam volatile.

Hence, $C \to II$

(D) Distillation under reduced pressure

Vacuum distillation is used for high-boiling substances that may decompose near their boiling point.

Glycerol from spent-lye is separated by distillation under reduced pressure because glycerol has a high boiling point and may decompose on ordinary heating.

Hence, $D \to I$

Final matching

$A-IV, \; B-III, \; C-II, \; D-I$

This corresponds to Option D.

Comparison with stored answer

Stored correct answer: D

Our derived answer: D

So the answer agrees with the stored answer.