List the gases h2o, he, hcl, brf, and no2 in order of increasing average molecular velocity at 25◦c. 1. rates of effusion: no2 < hcl < brf < he < h2o 2. rates of effusion: brf < no2 < hcl < h2o < he 3. rates of effusion: h2o < no2 < he < brf < hcl 4. rates of effusion: brf < h2o < hcl < no2 < he 5. rates of effusion: brf < he < hcl < h2 < no2 6. rates of effusion: he < brf < hcl < h2o < no2

I believe the answer is 2. Rates of effusion; BrF< NO2<HCl<H2O<He
According to the Graham's law o diffusion, the rate of diffusion of a fixed mass of a gas is inversely proportional to the square root of its molecular mass of its particles. The effusion rate for a gas depends directly on the average velocity of its particles. Therefore; the faster the gas particles are moving, the more likely they are to pass through the effusion orifice. Particles with a higher molar mass effuse more slowly than gases with a lower molar mass.