The correct answer is A. the stator current will be zero.
When a synchronous motor is running on no load, the rotor is not turning and there is no torque being produced. This means that there is no need for any current to flow in the stator windings, and the stator current will be zero.
Option B is incorrect because the stator current will not be very small. Even though there is no torque being produced, there is still a small amount of current that flows in the stator windings in order to maintain the magnetic field.
Option C is incorrect because the stator current will not be very high. The stator current is only high when the motor is producing torque. When the motor is running on no load, there is no torque being produced and the stator current will be zero.
Option D is incorrect because the back emf will not be more than the supply voltage. The back emf is the voltage that is induced in the stator windings by the rotating magnetic field. The back emf always opposes the applied voltage, and it will never be more than the applied voltage.