Helium gas has a molar mass of 4 g/mol. oxygen gas has a molar mass of 32 g/mol. how much faster or slower would helium effuse than oxygen from a small opening

According to Graham's Law of Diffusion,"the rates of diffusion of two gases are inversely proportional to the square root of their Molar masses or Densities at the same pressure and temperature".

                                     r₁ / r₂  =  
Where,
            r₁  =  Rate of Helium

            r₂  =  Rate of Oxygen

            M₂  =  Molar mass of Oxygen  =  32 g/mol

            M₁  =  Molar mass of Fluorine  =  4 g/mol

Putting values,

                                           r₁ / r₂  =  

                                           r₁ / r₂  =  

                                           r₁ / r₂  =  2.82
Result:
            Helium gas effuses 2.82 times faster than Oxygen gas.

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.