The upper frequency limit of the audible range of human hearing is about 20 kHz.

Explanation:
Human beings have the ability to hear sounds within a certain range of frequencies. This range is known as the audible range. The audible range of human hearing typically extends from about 20 Hz to 20,000 Hz, although it can vary slightly from person to person.

The audible range can be divided into different frequency bands, each of which corresponds to a different pitch or tone. Sounds with frequencies below 20 Hz are known as infrasound, and sounds with frequencies above 20,000 Hz are known as ultrasound.

The upper frequency limit of the audible range, which is about 20 kHz, is the highest frequency that most people can hear. As we age, our ability to hear high-frequency sounds tends to diminish, and many adults are unable to hear frequencies above 15 kHz or even lower.

The reason for this upper limit is due to the physiology of the human ear. The human ear is made up of several intricate structures, including the outer ear, middle ear, and inner ear. These structures work together to capture and transmit sound waves to the brain for interpretation.

The inner ear contains the cochlea, which is responsible for converting sound waves into electrical signals that can be processed by the brain. The cochlea contains tiny hair cells that vibrate in response to different frequencies of sound. These hair cells are more sensitive to lower frequencies and become less sensitive as the frequency increases.

Therefore, when the frequency of a sound wave exceeds the upper limit of the audible range, the hair cells in the cochlea are not able to vibrate with enough intensity to trigger the electrical signals needed for hearing. This is why frequencies above 20 kHz are generally considered to be outside the range of human hearing.

In conclusion, the upper frequency limit of the audible range of human hearing is about 20 kHz. This limit is determined by the sensitivity of the hair cells in the cochlea to higher frequencies.