Graham's law governs gas diffusion rates in the tube

Steps:

• Calculate molar masses: ethylamine (C₂H₅NH₂) = 45 g/mol; HCl = 36.5 g/mol.
• Apply Graham's law: diffusion rate ∝ 1/√(molar mass), so HCl (lighter) diffuses faster than ethylamine.
• HCl travels farther from its end, so the gases meet closer to the ethylamine end, forming the solid ring there.
• Position A is nearest the ethylamine source, matching the meeting point.

Why A is correct:

• HCl's faster diffusion shifts the reaction zone toward the slower-diffusing ethylamine end, per Graham's law.

Why the others are wrong:

• B: Midway assumes equal diffusion rates, ignoring molar mass differences.
• C: Closer to HCl end would require ethylamine to diffuse faster, which it doesn't.
• D: At HCl end ignores ethylamine's diffusion entirely.

Final answer: A