Frequency can be divided into three categories based on their frequency range:
Audible sound waves: The frequency range of this wave is 20Hz - 20000Hz. Humans can easily detect these types of waves.
Example: Sound produced by Vocal cords.
Infrasonic waves: The frequency range of these types of waves is below 20Hz. Humans cannot detect it.
Example: Elephants, Sound produced by Earthquake, Volcanic eruption and ocean waves, Weather, Lee waves, Avalanche, Waterfalls, Meteors, Lightening, etc.
Ultrasonic waves or Ultrasound waves: The sound frequency above 20,000Hz is known as ultrasonic waves. Humans cannot detect it too.
Examples: dog whistle, Dolphins, Bats, Porpoises, and Rats are examples of an Ultrasound wave.
EXPLANATION:
From the above discussion, we can say that the infrasonic sound is produced by elephants. So option 3 is correct.