Which of the following would support the conclusion that a solid sample is a mixture?

The property that would support the conclusion that a solid sample is a mixture is the melting range. If the solid has a melting range, it means that it is composed of two or more substances with different melting points. A pure substance always has a specific melting point, so if the solid has a range of melting points, it must be a mixture of different substances. The other properties do not necessarily indicate that a solid is a mixture. For example, the fact that a solid can be ground to a fine powder only suggests that it is a physical property of the substance. The density of a solid also cannot be used to determine if it is a mixture or not. Likewise, the ability of a solid to absorb moisture from the atmosphere does not necessarily indicate that it is a mixture, as many pure substances are hygroscopic and can absorb moisture from the air. Therefore, the correct answer is the third option: the solid has a melting range of 300oC to 375oC, as this indicates that the solid is not a pure substance, but rather a mixture of substances with different melting points.