The purity of a solid sample can best be determined by its?

1. Analyze the question You are asked which physical property best shows whether a solid is pure.

2. Explain the concept A pure crystalline solid melts sharply at one fixed temperature. For example, pure ice melts at exactly 0 °C at standard pressure. If impurities are present, two things happen:

• The melting point is lowered (melting point depression).
• The solid melts over a range of temperatures instead of at a single sharp point.

So a sharp, correct melting point means the sample is pure, while a low or wide melting range means it is impure.

3. Check each option

• A. Boiling point: This is used for purity of liquids, not solids. It is not the best choice for a solid sample.
• B. Melting point: This is the standard test for the purity of a solid. It is easy to measure and sensitive to impurities.
• C. Conductivity: This depends on whether the substance has mobile ions or electrons. It says nothing reliable about purity.
• D. Solubility: This varies with solvent and temperature, and it is not a precise purity test.

4. Answer The correct option is **B.

5. Exam tip Remember: "Solid → Melting point, Liquid → Boiling point." If a question asks about the purity of a solid, think "sharp melting point." If it asks about a liquid, think "fixed boiling point."