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. They raise the boiling point
- B. They lower the boiling point
- C. They have no effect
- D. They make it boil at a variable temperature
Answer
The correct answer is They make it boil at a variable temperature. 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 make it boil at a variable temperature. 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 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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