Q. A certain gas takes three times as long to effuse out as helium. Its molecular mass will be :
A) 27 u
B) 36 u
C) 64 u
D) 9 u
Explanation
[Solution from source] By Graham's law, effusion time ∝ √M, so t/t_He = √(M/4) = 3, giving M = 36 u. Assuming time is proportional to M itself would give 12 u, and squaring wrongly gives 9 u. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.