What units are used in frequency?

A sound’s loudness is measured in decibels (dB). Therefore option 1 can’t be the unit of frequency of a sound wave. The loudness of sound is determined by the intensity of the sound waves.

Frequency is expressed in units of hertz (Hz) which is equivalent to one (event) per second.

Frequency’s units are per second, written s-1 or hertz, Hz. Hertz and per second are identical units, i.e. 1 s-1 = 1 Hz . When describing a moving wave, frequency means the number of peaks which pass a stationary point in a given amount of time.

s-1. Unit of time, second (s): Second is the SI unit of time and is defined by taking the fixed value of Cesium frequency. It is expressed as s1.