Under identical conditions, r2r1=M1M2 As rate of diffusion is also inversely proportional to time, we will have, t1t2=M1M2 (a) Thus, For He, t2=24(5s)=52s=10s; (b) For O2,t2=232(5s)=20s (c) For CO,t2=228(5s)=25s; (d) For CO2,t2=244(5s)=55s