In a room, the reflected sound reaches the ear 0.05 s after its production. Will it produce an echo or reverberation? Justify your answer.

The reflected sound will produce a reverberation, not an echo. This is because for an echo to be heard, the time gap between the original sound and the reflected sound must be at least 0.1 s, so that the brain can distinguish them as two separate sounds. Here, the reflected sound reaches the ear in only 0.05 s, which is less than 0.1 s, so the original and reflected sounds merge together and the sound appears to persist for a short time after the source has stopped, this phenomenon is called reverberation.