Which modulation method varies the frequency of an electromagnetic carrier according to the intelligence being transmitted?

Frequency Modulation (FM) is the correct choice because it specifically alters the frequency of a carrier wave in response to the amplitude of the input audio signal or intelligence being transmitted. In FM, the frequency of the carrier signal varies within a defined range, which corresponds to the instantaneous amplitude of the audio or data signal.

This method allows for improved sound quality and greater resistance to noise and interference compared to other modulation techniques. As the amplitude of the information signal increases, the frequency of the carrier wave increases, allowing for more information to be encoded within the carrier's frequency variations. This characteristic of FM makes it especially suitable for broadcasting music and speech with high fidelity.

Other modulation methods, such as Amplitude Modulation (AM), vary the amplitude of the carrier wave instead of its frequency, while Pulse Amplitude Modulation (PAM) involves discrete pulses' amplitude variation, and Phase Shift Keying (PSK) varies the phase of the carrier signal. Each of these methods has its own advantages and specific applications, but FM's fundamental principle of frequency variation directly in relation to the signal being transmitted is what distinguishes it in this context.