What is the unit of frequency?
(a). Hertz
(b). Joule
(c). Ohm
(d). Kilocalorie

- Hint: The unit Hertz (Hz) is used to measure the number of cycles occurring per second of a periodic motion or event. Since, by the definition of frequency, its measurement unit must have a dimension of , this problem can be solved by finding the unit in the given option which has the same dimensions

Complete step-by-step solution -
The frequency of a periodic motion or event is the number of cycles that the motion completes in one second.
Hertz (Hz) is the SI unit of frequency and has dimensions of second inverse (s-1).
Thus the correct answer is option A) Hertz.
The unit is named Hertz in the honor of a German physicist Heinrich Hertz.
$1Hz=\dfrac{\text{1 Cycle}}{1\text{ Second}}$
Additional information:
Hertz is most commonly used in the units for the frequencies of all waves. On the basis of their frequencies, electromagnetic waves are given different names such as infrared, ultraviolet, etc.
Thus, sound also being a wave, its frequency is measured in hertz.
The range of human hearing is from sound waves of 20Hz to 20,000 Hz. However, some other animals, like dogs, can hear even below 20Hz (called infrasonic sound) and some others like bats, can hear above 20000 Hz (called ultrasonic sound).

In musical instruments frequency determines the pitch of a sound. The higher the frequency, the higher is the pitch. For example, a sound with a low frequency has a low pitch and is termed as flat or bass. On the other hand a sound with a high frequency has a high pitch and is termed as a shrill sound. The middle C note on the keyboard has a frequency of 262 Hz.

Note: Students should not get confused when they see the word pitch instead of frequencies in some questions, as essentially both of them relate to the same thing that is cycles per second.