Answer: B (argon at 40 \(^\circ\)C). The rate of diffusion depends on two things: the mass of the gas particles and the temperature. Lighter particles move faster, and a higher temperature gives the particles more kinetic energy, so they spread out more quickly.
Compare the masses: argon has \(A_r = 40\), while carbon dioxide has \(M_r = 12 + 2(16) = 44\). Argon is lighter, so argon diffuses faster than carbon dioxide at the same temperature. That rules out both carbon dioxide options.
Between the two argon samples, the hotter one diffuses faster because its particles have more energy. So argon at 40 \(^\circ\)C diffuses most quickly, giving answer B. Common error: choosing the hottest gas (CO₂ at 40 \(^\circ\)C) without first comparing the masses.
Every O Level Pure Chemistry TYS MCQ solution video, plus full Sec 3 / Sec 4 topic recordings.
Find out more