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

(1) 12.25 u

(2) 6.50 u

(3) 25.00 u

(4) 50.00 u

(1) 12.25 u

(2) 6.50 u

(3) 25.00 u

(4) 50.00 u