What does the partial pressure of a gas mean?

• A. The pressure contributed by a single gas in a mixture of gases
• B. The total pressure of the gas mixture
• C. The pressure at which gas solubility ceases
• D. The pressure at which gas diffuses fastest

Answer: (A)

Partial pressure reflects how much pressure a single gas would exert if it were present alone in the same volume at the same temperature. In a gas mixture, each component contributes its own share to the total pressure, and the sum of those contributions equals the total pressure (Dalton’s law). The partial pressure of a given gas is that individual pressure, which can also be expressed as P_i = X_i × P_total or as P_i = n_iRT/V. This makes the option describing the pressure contributed by a single gas in a mixture the best choice. The total pressure is the sum of all partial pressures, not just one gas’s share; the other statements relate to solubility or diffusion rates rather than the meaning of partial pressure.