One of the criteria for confirming the purity of benzene is to determine its

Step 1: Analyze the question The question asks which physical property can be used to confirm that a sample of benzene is pure.

Step 2: The concept A pure substance has fixed, characteristic physical constants:

• A sharp, constant boiling point (benzene boils at about 80.1 °C)
• A sharp melting point (benzene melts at about 5.5 °C)

Impurities change these values. They usually make the boiling point rise and cause it to occur over a range of temperatures instead of at one fixed temperature. For this reason, boiling point and melting point are the standard criteria for purity.

Step 3: Check each option

• A. Heat capacity: This does depend on the substance, but it is not a standard or practical test of purity.
• B. Boiling point: A pure liquid boils at one fixed temperature at a given pressure. This is the standard purity test for liquids.
• C. Mass: Mass depends on the amount of sample, so it says nothing about purity.
• D. Colour: Benzene is colourless, but many impurities are also colourless, so colour cannot confirm purity.

Step 4: Answer The correct option is B. boiling point.

Exam tip: For any question on the purity of a liquid, think boiling point. For a solid, think melting point. Pure substances have sharp, fixed values, while impure ones have a range.