If a gas mixture has partial pressures p1, p2, and p3, how is the total pressure calculated?

• A. P = p1 × p2 × p3.
• B. P = p1 + p2 + p3.
• C. P is the average of partial pressures.
• D. P equals the largest partial pressure.

Answer: (B)

Gas mixtures follow Dalton's law: each component gas contributes its own partial pressure, and the total pressure is the sum of those contributions. So with p1, p2, and p3, the total pressure is P = p1 + p2 + p3. This reflects that each gas exerts pressure as if the others weren’t there, and those pressures simply add together to give the overall pressure in the container. Multiplying, averaging, or taking only the largest partial pressure would ignore the independent contributions of the other gases.