Option 1 states that bats can ascertain distances, directions, nature, and size of obstacles at night by the reflection of ultrasonic waves emitted from the bat itself. This means that bats emit ultrasonic waves, which bounce off objects in their surroundings and get reflected back to the bat. By analyzing the time it takes for the waves to return and the frequency of the returned waves, bats can determine the distance, direction, nature, and size of the objects.

Option 2 states that bats can ascertain these details by the reflection of ultrasonic waves from distant objects. This is incorrect because bats emit the ultrasonic waves themselves, and it is the reflection of their own waves that helps them navigate, not the reflection of waves from other objects in the distance.

Option 3 states that bats use supersonic waves emitted from themselves for navigation. Supersonic waves refer to waves that travel faster than the speed of sound. This is incorrect because bats actually use ultrasonic waves, which have frequencies higher than the range of human hearing, not supersonic waves.

Option 4 states that bats use supersonic waves emitted from distant objects for navigation. This is incorrect because bats rely on their own emitted ultrasonic waves and their subsequent reflection, not waves emitted by distant objects.

Therefore, option 1