What units are used in frequency?

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

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’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.