Here it says to rank the following in order of increasing rate of effusion. Remember we said that the higher the molar mass than the lower the speed or rate of a gas. So here if we take a look, O2 has two oxygens. The combined mass would be 32g per mole.
PF5 has one phosphorus and five fluorines. When you add the mall up together, it gives you approximately 125.97g per mole. Carbon dioxide weighs approximately 44.01 grams per mole. When you add up the one carbon and the two oxygen and then xenon. If you look on the periodic table, it has a weight of approximately 131, oh .29 grams per mole.
We want to do it in terms of increasing rate of effusion, which means we're going to start out with the heaviest, which has the slowest rate, all the way up to the lightest one, which has the highest rate. All right, so who has the highest molar mass or highest weight would be Xenon. Xenon will be the slowest and therefore lowest rate of effusion.
Then we have PF5, then we have CO2 and then O2 weighs the least out of everyone, so it would move the fastest. This would be our order going from the slowest rate of a fusion to the highest rate of fusion based on their individual molar masses.