Why is it necessary to liquefy air to separate its components?

It is important to liquefy the air to separate its component because the process of  separating air components requires distillation. To do this process air must be converted to its liquid form. Usually, this is done by filtering first the dust and then cooling the air at very low temperature. The process of separating air components is called fractional distillation. The liquefied air will pass into the bottom of a column. The columns will separate the oil fractions of liquefied air depending on the component in the air.

The correct answer would be b