A gas was found to diffuse twice as slow as helium. Based on molar mass, which of the following was the gas?

Question

Quizplus · Accepted Answer

The gas with twice the diffusion rate of helium would have a molar mass half of that of helium (as the diffusion rate is inversely proportional to the square root of molar mass). The molar mass of helium is approximately 4 g/mol. Out of the given options, only CH4 has a molar mass close to 2 g/mol (16 g/mol/4 = 4 g/mol, and 16 g/mol/8 = 2 g/mol). Therefore, the gas with twice the diffusion rate of helium must be methane (CH4).

A Gas Was Found to Diffuse Twice as Slow as Helium