Correct option is D
A synchronous motor can operate at all the power factors.
At normal excitation, synchronous motor works at the unity power factor.
If the field of a synchronous motor is under excited, then the power factor will be lagging and it acts as an inductor.
If the field of a synchronous motor is overexcited, then it acts as a synchronous capacitor and the corresponding power factor will be leading.
A synchronous motor running with no load will lead the current i.e. leading power factor like a capacitor. This synchronous motor running without load i.e. over-excited is synchronous condenser.
The synchronous condenser is used in power lines to improve power factor, power factor correction by connecting it along with transmission lines.
