Why is neutralization necessary for some vacuum-tube amplifiers?

In vacuum-tube RF amplifiers, the physical proximity of internal elements (like the plate and the grid) creates small, unintended capacitors. This phenomenon is known as interelectrode capacitance. At radio frequencies, this capacitance provides a pathway for the high-power output signal to leak back into the input grid. If the phase is correct, it creates positive feedback, turning the amplifier into an oscillator. Neutralization solves this by feeding a small, intentionally out-of-phase signal back to the input to perfectly cancel the unwanted feedback. The other options describe entirely different circuit problems. Neutralization has nothing to do with filtering AC hum from filament transformers, stopping grid-to-cathode leakage, or altering the loaded Q of the amplifier circuit.