Hertz is the unit of which of the following?
A) Wavelength
B) Amplitude
C) Frequency
D) None of these

Hint:Hertz can be written as the inverse of second. In SI base units, 1 Hertz = 1 s$^{ - 1}$

Complete step-by-step solution:
Hertz is the unit of frequency in SI units. It is defined as the number of cycles per second. The symbol Hz is used for hertz. Since, the number of cycles is a unit less number, and the unit of time is second, in SI base units, it can be written as 1 Hz = 1 s$^{ - 1}$. It was named after Heinrich Rudolf Hertz, who provided proof of the existence of electromagnetic waves.

The unit of wavelength is meter (m). Wavelength is the distance between two consecutive crests or troughs in a wave. Its unit is the same as the unit of length. However, smaller units of length such as angstrom, nanometer, micrometer, millimeter or centimeter are generally used to represent wavelength.

The unit of amplitude depends on the type of wave. For transverse waves, amplitude is measured in the unit of length. It is the measure of how much a wave gets disturbed from its mean position. More is the disturbance, higher is the amplitude.
Hence, the correct answer for this question is frequency.

Therefore, option C is the correct answer.

Note:The unit revolutions per minute (rpm) or revolutions per second (rps) is used for rotational speed or frequency of rotating systems. However, according to the International System of Units (SI), it is not a unit. 1 rpm = 60 Hz.