An unknown gas is found to diffuse through a porous membrane 4.11 times more slowly than h2 what is the molecular weight of the gas?

To answer this question, you need to know Graham's Law of Effusion/Diffusion formula. In this formula, the rate of diffusion/effusion would be influenced by the mass. As the molecule has bigger mass, the rate should be slower because it will be harder to pass the membrane. The calculation should be:
Rate 1 / Rate 2 = √[M2/M1] 
4.11/1= √[M2/2] 
M2=33.78 g/mol