Which of the following is a characteristic of carbon monoxide?

Carbon monoxide is indeed slightly less dense than air, which is a significant characteristic of this gas. The density of carbon monoxide is approximately 0.97 grams per liter, while the density of air is about 1.29 grams per liter. This difference means that carbon monoxide can accumulate in enclosed spaces, as it tends to rise and spread out, potentially leading to dangerous situations where it remains undetected.

Understanding the properties of carbon monoxide is crucial, especially in contexts like crime scene investigations where this gas might be involved in accidental poisoning or foul play. The other characteristics listed in the options do not accurately describe carbon monoxide; for instance, it is odorless, not highly flammable, and lighter than many gases, but not classified as heavy. This information helps in recognizing the dangers associated with carbon monoxide exposure and the importance of proper detection and monitoring in environments where it may be present.