Graham's Law of Diffusion Governs the Order

Steps:

• Apply Graham's law: rate of diffusion ∝ 1/√(molar mass).
• Calculate molar masses: CH4 = 16 g/mol, NH3 = 17 g/mol, CO2 = 44 g/mol, N2 = 28 g/mol.
• Determine square roots: √16 ≈ 4.00, √17 ≈ 4.12, √28 ≈ 5.29, √44 ≈ 6.63.
• Rank from slowest (highest √M) to fastest (lowest √M): CO2 (3), N2 (4), NH3 (2), CH4 (1).

Why C is correct:

• Graham's law dictates rates inversely proportional to √M, so heaviest CO2 diffuses slowest, followed by N2, NH3, then lightest CH4.

Why the others are wrong:

• A: Reverses order; CH4 diffuses fastest, not slowest.
• B: Starts with NH3; CH4 has lower mass, so faster diffusion.
• D: Places N2 first; CO2 has highest mass, so slowest.

Final answer: C