Assertion (A): For echo, sound should travel a minimum distance of atleast 33 m in air.

Reason (R): Distinct echo requires a minimum time delay of 0.1 s.

1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true and R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true

Both A and R are true and R is the correct explanation of A

Explanation

Assertion (A) is true because the speed of sound in air is about 330 m s^-1, and for an echo to be heard distinctly, a minimum time gap of 0.1 s is required.

In this time, sound travels a total distance of:

330 × 0.1 = 33 m

Since this distance includes the to-and-fro journey of sound, the reflecting surface must be at least 16.5 m away.

Thus, the total distance travelled by sound is about 33 m.

Reason (R) is true because a distinct echo requires a minimum time delay of 0.1 s, which is the persistence of hearing of the human ear.

The Reason justifies the Assertion because a distinct echo needs a time gap of 0.1 s. In this time, sound travels about 33 m (to and fro) which leads to a minimum distance of about 16.5 m to the reflecting surface, explaining the assertion.

Therefore, both A and R are true and R is the correct explanation of A.