The correct answer is B. X Ã Y.
The power gain of an amplifier is the ratio of the output power to the input power. It is a measure of how much the amplifier amplifies the power of the input signal.
The current gain of an amplifier is the ratio of the output current to the input current. The voltage gain of an amplifier is the ratio of the output voltage to the input voltage.
The power gain of an amplifier can be calculated using the following equation:
Power gain = Current gain à Voltage gain
Therefore, if the current gain of the amplifier is X and its voltage gain is Y, then its power gain will be X Ã Y.
Option A is incorrect because it is the reciprocal of the power gain. Option C is incorrect because it is the sum of the current gain and the voltage gain. Option D is incorrect because it is the difference between the current gain and the voltage gain.