Two gases A and B having the same volume diffuse through a porous in 20 and 10 seconds respectively .The molecular mass of A is 49u.Molecular mass of B will be

Answer 1

Choose any convenient volume size, say 1 L.
rate A = 1L/10 sec
rate B = 1L/20 sec

(rate1/rate2) = sqrt(M2/M1)
Substitute and solve for M2.

Answer 2

25.00u