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. It remains the same
- B. It increases
- C. It decreases
- D. It becomes unpredictable
Answer
The correct answer is It becomes unpredictable. 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 It becomes unpredictable. 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
Confusing Boiling Points
Students often think that a substance can be identified as pure if it boils at any temperature within a range.
Remind students that a pure substance has a specific boiling point, and deviations from this indicate impurities.
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