A. 100%
B. 50%
C. 25%
D. 0%
Answer: D. 0%
Explanation:
The speed regulation of a motor expresses how much its speed varies between no-load and full load.
The synchronous motor runs at a constant speed whose magnitude is dependent on supply frequency and the number of poles.
The steady-state speed of the motor is constant from no load to the maximum torque that the motor can supply (called pull-out torque).
Since the speed of the motor is constant hence its speed regulation is zero.