[wqxt]

Why is benzyl viologen a better oxidant than methyl viologen ?

[cth]

Because the radical electron from the viologen can be delocalized over the benzyl moiety in addition to the pyridine part. It is not the case for the methyl.

As more delocalization results in better stability for radical electrons, the benzyl viologen is more stable than the methyl one. It is easier to form.

[wqxt]

Can it still be delocalized although it's separated by a CH2 group (unless I'm looking at the wrong structure) ?