oscillator
power amplifier
A transistor amplifier with a tank circuit and positive feedback will act as an oscillator, not a power amplifier or a voltage amplifier. The tank circuit typically consists of a capacitor and an inductor that form a resonant circuit. When positive feedback is applied to this circuit, it results in sustained oscillations.
In the case of a transistor amplifier, positive feedback helps in producing continuous oscillations, which is the characteristic behavior of an oscillator. Oscillators are used in applications such as signal generators, radio frequency (RF) generation, etc.
However, the other options are incorrect because:
Correct Answer: (A) Oscillator