Scoring scheme: 3-3-2-1 when you use the half reaction method to balance the redox reaction between one mole of nbs and ascorbic acid to give l-dehydroascorbic acid and succinimide, how many moles of electrons are transferred?

In the redox reaction between one mole of NBS and ascorbic acid, ascorbic acid undergoes oxidation reaction to form L-dehydroascorbic acid.

On other hand, N-bromosuccinimide (NBS) undergoes reduction to form succinimide.

Electron transferred during this process is two. Complete reaction is attached below for quick reference.

Thus, one molecule of NBS reacts with one molecule of ascorbic acid, during this redox reaction. For each molecule reacting, two electrons are transferred. 

Thus, when one mole of NBS reacts with one mole of ascorbic acid, 2 x Na moles of electrons will be transferred. It may be noted here that, Na = Avagadro's number = 6.022 X 10^23.