Agent concentration is defined as the portion of agent in an air mixture expressed in which unit?

• A. Mass percent
• B. Mole percent
• C. Volume percent
• D. Weight percent

Answer: (C)

Concentration of a clean agent in air is described as a volume percent. This expresses how much of the total air volume is occupied by the agent, which is the most practical and meaningful way to quantify a gas in a mixture. Because gases obey the idea that volume is proportional to the number of moles (Avogadro’s law), the volume fraction is essentially the same as the mole fraction under typical conditions, making volume percent a natural and consistent metric. It also avoids the complications of mass or weight-based percentages, which depend on molecular weight and change with temperature and pressure. So, expressing concentration as a volume percent (percent by volume) is the standard approach.