Compared to a cooler water sample, warmer water has which of the following characteristics?

Warmer water is indeed characterized by its reduced capacity to hold dissolved oxygen compared to cooler water. As temperature increases, the solubility of gases, including oxygen, decreases. This is a fundamental principle in chemistry and is particularly important in aquatic ecosystems, where oxygen is crucial for the survival of fish and other aquatic organisms. When temperatures rise, the reduced oxygen levels can lead to stress for these organisms and can affect their overall health and populations.

The other characteristics, while they may apply to different contexts, do not accurately describe the properties of warmer water in comparison to cooler water. For instance, the statement regarding vapour pressure suggests that warmer water has a lower vapour pressure, which contradicts the principle that warmer temperatures actually increase the vapour pressure of liquids. Similarly, the density of water decreases as it warms, which does not align with the notion of warmer water being more dense. Lastly, while warmer water can sometimes contribute to pollution depending on other factors, it is not classified as a major pollutant in itself. Thus, the most accurate characteristic pertaining to the comparison of warmer and cooler water is that warmer water cannot hold as much dissolved oxygen.