To determine which substances are pure based on the given data, we need to look for a specific temperature range for both melting and boiling points for each substance.
Based on the table provided:
Substance A has a melting range of 10-15 degrees and a boiling range of 40-50 degrees.
Substance B has a melting point of 65 degrees and a boiling point of 180 degrees.
Substance C has a melting point of 129 degrees and a boiling point of 204 degrees.
Substance D has a melting range of 90-97 degrees and a boiling range of 310-314 degrees.
A pure substance typically has a specific, well-defined melting point and boiling point. In this case, substances B and C have specific temperature values for both melting and boiling points. Therefore, substances B and C can be considered pure.
Substances A and D, on the other hand, have melting and boiling ranges, indicating that they consist of impure mixtures of different substances. When a substance is impure, it can have a range of melting and boiling points due to the presence of various components with different melting and boiling points.
In summary, substances B and C are pure, while substances A and D are impure.
I hope this helps.