Question detail
Which answer avoids confusing pure substance with another qualitative analysis result?
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. They increase the melting point.
- B. They decrease the melting point.
- C. They have no effect on the melting point.
- D. They make the melting point unpredictable.
Answer
The correct answer is They decrease the 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 They decrease the melting point.. Use this as an exam check: if the observation is not purity evidence, the conclusion about pure substance is not properly supported. Other options are weaker when they confuse gas tests, flame colours, ion-test precipitates, chromatography evidence, or pure-substance/formulation wording.
Common mistake
Identifying Purity from Melting Points
Students often think that a substance is pure if it has a melting point that matches the literature value, without considering the possibility of impurities affecting the melting point.
Students should remember that impurities can lower or raise the melting point, and they should analyze the melting point range to determine purity.
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