Concept:A pure substance has fixed physical properties such as a definite boiling point.Explanation:Pure benzene has a specific boiling point at a given pressure.If impurities are present, the boiling point changes from this fixed value.Therefore, determining the boiling point helps confirm whether benzene is pure.Mass and colour are not reliable tests for purity.Heat capacity is also not a standard criterion for purity testing.Answer:B. boiling point