Final answer:
Density varies by state of matter, with gases being least dense, followed by solids, and liquids being the most dense; temperature and pressure also affect density.
Step-by-step explanation:
The density of a substance can vary depending on its state of matter. For instance, water represents a unique case where the solid state (ice) is less dense than the liquid state. This behavior allows ice to float on water. In general, gases have the lowest density, as their particles are far apart with large amounts of empty space. Conversely, the particles in liquids and solids are much closer together, leading to similar densities between these two states, which are much higher than that of gases. Factors such as temperature and pressure also impact the density of a substance, with the density normally increasing as the temperature decreases for solids and liquids, while it varies significantly for gases based on these conditions.