The compound that is most. reactive toward electrophilic nitration is:

The compound that is most. reactive toward electrophilic nitration is: toluene.

The electron density that is present on a substance affects how reactive it is to electrophilic nitration. The chemical will be more reactive to electrophilic nitration the greater the electron density.
Because the presence of the methyl group causes an electron-donating action that raises the electron density, toluene is most reactive in this situation towards electrophilic nitration.

Hence, option A is correct.