Bats have a unique ability to navigate and detect obstacles in their path, even in complete darkness. They achieve this through a process known as echolocation, where they emit high-frequency sound waves and listen for the echoes that bounce back off objects in their environment.

Option 1: Infrasonic waves refers to sound waves that are below the range of human hearing. Bats, on the other hand, use ultrasound, which are sound waves with frequencies higher than what humans can hear. So, option 1 is incorrect.

Option 3: Radio waves are electromagnetic waves and are not used by bats for echolocation. Bats rely on sound waves and not radio waves to navigate, so option 3 is incorrect.

Option 4: Microwaves are electromagnetic waves with significantly higher frequencies than those used by bats. Hence, option 4 is incorrect.

The correct answer is option 2: Ultrasonic waves. Bats emit these high-frequency sound waves and listen for the echoes that bounce back to detect obstacles in their path. By analyzing the time it takes for the echoes to return and their intensity, bats can determine the location, size, and shape of objects around them, allowing them to navigate and hunt efficiently even in the darkness.