What is the lowest limit of frequency range that is audible to human beings ?

Answer

20 Hz

Explanation

Ultrasonic and infrasonic sounds are the inaudible sounds to human beings.
Ultrasonic sounds have frequencies greater than 20 kz (i.e, `gt` 20,000 vibrations per second).
Infrasonic sounds have frequencies lesser than 20 Hz (i.e., `lt` 20 vibrations per second).