What does "density" refer to?

Density is a fundamental concept that refers to the mass of a substance divided by its volume. It is commonly expressed as mass per unit volume, which is typically specified under standard temperature and pressure conditions to ensure consistency in measurements. Understanding density is crucial in various applications, including fire and explosion investigations, as it can help determine the behavior of materials during combustion and their potential contribution to fire dynamics.

For instance, knowing the density of a flammable liquid can aid in predicting how it will spread in a fire scenario, as liquids with lower densities may float on water, affecting fire spread and behavior. Hence, option B accurately captures this definition, making it the correct choice.