Question detail
In Pure substances, which answer best matches the evidence for pure substance?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Purity, formulations and chromatography
Question
- A. If it melts over a range of temperatures
- B. If it has a sharp melting point
- C. If it melts at a temperature lower than expected
- D. If it boils at a range of temperatures
Answer
The correct answer is If it has a sharp melting point. It matches pure substance because the evidence is single element or compound / fixed melting point and the expected result is purity evidence.
Explanation
The correct option is If it has a sharp melting point. This is correct because single element or compound / fixed melting point is the evidence expected for pure substance, and purity evidence is the result that supports the conclusion. Other options are weaker when they confuse gas tests, flame colours, ion-test precipitates, chromatography evidence, or pure-substance/formulation wording.
Common mistake
Misunderstanding Melting and Boiling Points
Students often think that all substances melt and boil at the same temperature regardless of purity.
Remember that a pure element or compound has specific melting and boiling points, while impurities can alter these temperatures.
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