Answer: Both gases have the same average kinetic energy per molecule.
- A Both gases have the same rms speed
- B Both gases have the same average kinetic energy per molecule
- C The heavier gas molecules have higher rms speed
- D Both gases have the same pressure individually inside the mixture
Correct answer: B. Both gases have the same average kinetic energy per molecule
Explanation: At a given temperature, average KE per molecule = (3/2)k<sub>BT</sub> is the same for all ideal gases regardless of molar mass; only their speeds differ (lighter molecules move faster).
Not all gas molecules move at the same speed - the Maxwell-Boltzmann distribution shows the spread, with the most probable speed vp slightly less than the average vavg, which is slightly less than the root-mean-square speed vrms used in the pressure formula.
Concept context
Kinetic theory of gases connects molecular motion to pressure and temperature, explaining gas laws, specific heats, and molecular speeds.