Final answer:
Frequency in the context of sound refers to the number of vibrations per second, measured in hertz (Hz), and determines the pitch of a sound. Higher frequencies correspond to higher pitches, while lower frequencies correspond to lower pitches.
Step-by-step explanation:
In determining pitch, frequency refers to the number of vibrations per second. This means the correct answer to the question is D) Number of vibrations per second. Frequency is a crucial aspect of sound waves and is measured in hertz (Hz).
A higher frequency indicates a higher pitch, such as the chirp of a bird, while a lower frequency indicates a lower pitch, like the roar of a lion. It must be noted that the perception of frequency is termed pitch, which is not significantly affected by other physical quantities like intensity.
The word loudness of sound is described by its intensity level or decibel, not frequency. Therefore, 'b. intensity level or decibel' is the correct option for describing loudness. The quality of a sound, known as timbre, is affected by the sound wave's frequency, amplitude, and timing, but timbre is not the same as pitch.