A student carries out an experiment to determine the melting point of a waxy solid. She heats a sample until it melts, then measures and records its temperature as it cools down. Explain how the student could use her results to decide whether the waxy

...solid is a pure substance or a mixture.
Firstly, she would need to plot a graph of temperature against time. Temperature remains constant at the melting point. The graph will show whether the solid is pure or a mixture. A pure substance will give a sharp melting point, meaning the graph line will be horizontal. Whereas, a mixture melts over a range of temperatures meaning that the graph line will not be horizontal.