WAEC Chemistry 2017 Paper

Concept:Fractional distillation separates gases based on differences in their boiling points.Explanation:Air is first cooled until it becomes a liquid.The liquid air is then gently warmed inside a fractionating column.Nitrogen has a lower boiling point ($-196^\circ C$) than oxygen ($-183^\circ C$).So nitrogen boils off first as a gas, while oxygen remains liquid.These gases are collected separately because they turn into vapour at different temperatures.This shows that the separation is possible due to the difference in boiling points.Answer:C. of the difference in their boiling points