ANS:A - at maximum negative

Make 3 steps at angles of 90 degrees:

1. Plane is in parallel with flux lines so angle = 0.

2. Plane cuts perpendicularly the flux lines at an angle = 90 (until here current is in 1 direction maximum positive).

3. Going to 180 becoming parallel again with flux lines max. Positive induced voltages will decrease to zero because angle = 180.

4. Again going to 90 turn from this 180 position the voltage induced will be negative at maximum.

Maximum positive value of voltage is induced when the face/plane of armature cuts the flux lines at 90 degrees so again coming to this very angle of 90 by completing a turn of 180 will induce max negative voltage.