Dalton's Law of Partial Pressures states that the total pressure of a gas mixture is the sum of the partial pressures of its components.

• A. P_total = P1 + P2 + P3
• B. P_total = nRT/V
• C. P_total = P1 × P2 × P3
• D. P_total = kT

Answer: (A)

Think about how gases in a mixture contribute to pressure: each gas pushes on the container with a pressure it would exert by itself. Dalton’s law says you add those contributions to get the total pressure. For three components, the total pressure is the sum of the three partial pressures: P_total = P1 + P2 + P3.

This directly expresses the additive nature of partial pressures. It also connects to the ideal gas law: for each component, Pi = ni RT / V, so summing gives P_total = (n1 + n2 + n3) RT / V, showing the same result from a different angle. The key point is that the total pressure is the sum of the individual pressures, not their product or some other operation.

The other forms don’t reflect this additivity. A product of partial pressures isn’t how pressures combine, and P_total = kT lacks dependence on volume and amount of gas, so it doesn’t describe a gas mixture’s pressure.