If in a synchronous motor, driving a given mechanical load and drawing current at a leading power factor from constant voltage supply its field excitation is increased, its power factor

A leading power factor is desirable in many applications, as it means that the motor is helping to improve the overall power factor of the system.

Option B is incorrect, as increasing the field excitation will cause the motor to draw more current, not less.

Option C is incorrect, as increasing the field excitation will cause the power factor to become more leading, not remain unchanged.

Option D is incorrect, as the correct answer is A.