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The correct answer to this question can be understood by looking into how frequency deviation is measured in the context of frequency modulation (FM) and reactance modulation.

In a frequency modulation system, frequency deviation refers to the maximum shift away from the nominal carrier frequency due to modulation. It is typically represented in kilohertz (kHz) or hertz (Hz) and quantifies how much the frequency of the carrier wave varies in response to an input signal.

For the scenario given, where a 12.21-MHz reactance-modified oscillator feeds into a 146.52-MHz FM phone transmitter with a specified deviation of 5 kHz, we need to calculate the resulting frequency deviation.

The 12.21 MHz oscillator contributes to the overall modulation of the carrier frequency (146.52 MHz) through reactance modulation. Here, the frequency deviation is based on the modulation index, which is the ratio of the frequency deviation to the modulating frequency. The desired modulation creates a deviation that must correlate with the input oscillator’s characteristics.

Calculating the deviation relative to the carrier's frequency means knowing how the modulating signal at 12.21 MHz interacts with the overall system, defining how many cycles of modulation fit into the carrier's cycles