Explanation:

- When a firecracker is set off in front of a cliff, the sound travels to the cliff and back.

- The total time for the sound to make this round trip is 5 seconds.

- Speed of sound is 340 m/s, which means sound covers 340 meters in one second.

- Total distance traveled by the echo is: Speed × Time = 340 m/s × 5 s = 1700 meters.

- This total distance includes both the distance to the cliff and back.

- Therefore, the one-way distance to the cliff is 1700 meters divided by 2, which is 850 meters.

Correct Answer: Option 4 - 850 m