The rate of diffusion of gases increases with increase(s) in I. density II. temperature III, mass. Which is/are correct?

Analyze the question: We need to find which factors make gases diffuse faster. The statement is "rate of diffusion increases with an increase in..." density, temperature, or mass.

Concept:

• Graham's law of diffusion: the rate of diffusion of a gas is inversely proportional to the square root of its density (or molar mass).

Rate ∝ 1/√ρ

So a denser gas diffuses more slowly, and a heavier gas (greater mass of molecules) also diffuses more slowly.

• Temperature: raising the temperature increases the average kinetic energy and speed of the molecules (v ∝ √T), so they spread out faster.

Step-by-step evaluation:

• I. Density: increasing density decreases the rate of diffusion. Not correct.
• II. Temperature: increasing temperature increases the rate of diffusion. Correct.
• III. Mass: heavier molecules move more slowly at the same temperature, so the rate decreases. Not correct.

Only statement II is correct.

Answer: B. II only.

Tip: Remember "light and hot diffuse fast". Low density, low molar mass and high temperature all speed up diffusion. When a question says "increases with increase in density or mass", it is almost always a trap, because the relationship is inverse.