Why the need to use right rudder during stall recovery?
You wrote:

When recovering from a stall, you need to add power. The increased power induces a torque in the opposite direction.
My problem with this answer is that torque will result in roll and usually ailerons are used to control the roll. Why rudder in this case?

I think you already know that a stall happens when you no longer have smooth airflow over the wings. Because you don't have effective airflow over the wings, your ailerons are not working. (they may be partially effective, or have no effect at all)
You are right that ailerons are used to control roll during nominal flight; but a stall is not nominal, and the ailerons are no longer effective.
The rudder, as a vertical surface, is not stalled the same way that the wings are.  So while it may not be the ideal way to counter a roll moment, its more reliable than the ailerons.