SI unit of frequency:-

The correct answer is hertz.

Key Points 

Frequency: The number of vibrations at which sound waves travel per second is called the frequency of the sound wave.

• It is denoted by f or ν. 
• The SI unit of frequency is Hertz (Hz).
• The Hertz is the standard unit for measuring the frequency of a wave.
• One Hertz is equal to one cycle per second.
• Frequency is the number of occurrences of a repeating event per unit of time.
• It is also referred to as temporal frequency, which emphasizes the contrast between spatial frequency and angular frequency.
• Frequency is measured in units of hertz which is equal to one occurrence of a repeating event per second.
• The formula of Frequency is f = 1/T (f =frequency and T = period).

 Additional Information