[toadesque]

1. If you had a mixture of benzene, toluene, and m-xylene, what would be the expected order of retention times? Explain.

I said that the order would be 1. benzene, 2. toluene, and 3. xylene

But I don't understand how to draw that conclusion. Why does the order come out that way? (regardless if I'm right or wrong)

[a student]

the only difference which I realize is the mass of them, I mean xylene is heavier than toluene and that is heavier than benzene.

[lavoisier]

1. If you had a mixture of benzene, toluene, and m-xylene, what would be the expected order of retention times? Explain.

I said that the order would be 1. benzene, 2. toluene, and 3. xylene

But I don't understand how to draw that conclusion. Why does the order come out that way? (regardless if I'm right or wrong)

From your description, one only knows that you're talking about a chromatographic separation of 3 very similar aromatic hydrocarbons.
Shouldn't you specify what kind of chromatographic method you're talking about? GC? Reverse phase HPLC? TLC?

Once you know that, you can reason about the type of equilibrium between your stationary phase and mobile phase, and see if the 3 compounds should be expected to behave differently...
The most important thing, as always, is to formulate the problem as clearly as possible. That makes much easier to find your way to the solution.