Answer:
"frequency of vibrations"
Explanation:
The pitch of a sound is defined as the quality that is responsible to judge any sound. The pitch of a sound is most closely related to the frequency of vibrations. Pitch is directly related to the frequency of the sound wave.
If the pitch is high, it will have high frequency and if the pitch is low, it will have low frequency. But the loudness of sound depends on the amplitude of the sound wave. The energy of the wave defines the loudness of the wave.
Hence, the correct option is (a) "frequency of vibrations".
