Concept:Air is a mixture of gases with different boiling points.
They can therefore be separated by fractional distillation of liquid air.
Explanation:The most suitable method is the fractional distillation of liquid air.
This works because nitrogen, oxygen, and other gases in air boil at different temperatures.
First, air is filtered to remove dust and purified.
It is then cooled under high pressure until it turns into liquid air.
Water vapour and carbon dioxide freeze out as the temperature drops.
The liquid air is allowed into a fractional distillation column.
As the liquid air warms, each gas changes to vapour at its own boiling point.
Nitrogen escapes first at the top of the column, followed by argon and then oxygen.
By collecting each gas at the correct level, pure gases such as nitrogen and oxygen are obtained.
Answer:B. Fractional distillation of liquid air.