The correct answer is: B. inversely proportional to the synchronous reactance
The synchronous reactance is a measure of the opposition of a synchronous machine to the flow of alternating current. The greater the synchronous reactance, the more difficult it is to get the machine to synchronize with the power grid. The synchronizing power of a synchronous machine is the amount of power required to bring the machine up to speed and synchronize it with the power grid. The synchronizing power is inversely proportional to the synchronous reactance, which means that the greater the synchronous reactance, the less synchronizing power is required.
Option A is incorrect because the synchronizing power is inversely proportional to the synchronous reactance, not directly proportional.
Option C is incorrect because the synchronizing power is not equal to the synchronous reactance.
Option D is incorrect because the synchronizing power is not none of the above.