Ptotal = P1 + P2 + P3 +…………. Pn, is an expression of law

Step 1: Analyze the question The expression P_total = P₁ + P₂ + P₃ + … + Pₙ says that the total pressure is the sum of individual pressures. This describes gases in a mixture.

Step 2: Explain the concept Each gas in a mixture exerts its own pressure, called its partial pressure. This is the pressure it would exert if it alone occupied the container at the same temperature. The total pressure of the mixture is the sum of all these partial pressures. This is Dalton's Law of Partial Pressures.

Step 3: Check the other options

• A. Boyle's law: PV = constant (at constant temperature). It relates pressure and volume of a fixed mass of gas.
• B. Charles' law: V/T = constant (at constant pressure). It relates volume and temperature.
• D. Graham's law: Rate of diffusion ∝ 1/√(molar mass). It deals with diffusion and effusion.
• E. Gay-Lussac's law: P/T = constant (at constant volume). It relates pressure and temperature. It is also used for combining volumes of gases.

None of these involves adding pressures of different gases.

Step 4: Example If a container holds oxygen at 200 kPa and nitrogen at 300 kPa, then: P_total = 200 + 300 = 500 kPa

**Answer: C.

Tip: Think "D for Dalton = Different gases adding up." Whenever you see partial pressures or a sum of pressures in a mixture, choose Dalton.