Which of the following best explains why some substances float on water?

• A. They are insoluble in water.
• B. They have a higher boiling point than water.
• C. They have a lower density than water.
• D. They contain more hydrogen atoms than water.

Answer: (C)

Verified step by step guidance

1. Understand the concept of density, which is defined as mass per unit volume, mathematically expressed as \(\text{density} = \frac{\text{mass}}{\text{volume}}\).
2. Recognize that whether a substance floats or sinks in water depends on its density relative to the density of water. If the substance's density is less than that of water, it will float; if greater, it will sink.
3. Analyze the options given: Insolubility in water does not guarantee floating, as some insoluble substances can sink; boiling point is unrelated to floating behavior; the number of hydrogen atoms does not directly affect density or buoyancy.
4. Conclude that the best explanation for why some substances float on water is that they have a lower density than water, allowing them to be buoyant and stay on the surface.
5. Summarize that floating is a physical property related to density differences, not solubility, boiling point, or molecular composition in terms of hydrogen atoms.