Question detail
A student is testing pure substance. Which choice keeps the observation and conclusion correctly linked?
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. A pure substance has a uniform composition.
- B. A mixture has a fixed composition.
- C. A pure substance can be separated by physical means.
- D. A mixture has a single melting point.
Answer
The correct answer is A pure substance has a uniform composition.. 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 A pure substance has a uniform composition.. The important distinction is that pure substance must be identified from single element or compound / fixed melting point; answers that swap in a different test or result do not match Pure substances. Other options are weaker when they confuse gas tests, flame colours, ion-test precipitates, chromatography evidence, or pure-substance/formulation wording.
Common mistake
Misunderstanding Pure Substances
Students often think that a pure substance can contain small amounts of impurities and still be considered pure.
A pure substance must be a single element or compound with no other substances mixed in.
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