Which property of sound leads to the formation of echoes?

(i) Which property of sound leads to the formation of echoes? Briefly explain.
(ii) What will happen, if the reverberation time in a big hall is too long?

(i) The property which leads to the formation of echoes is reflection of sound. When a sound is repeatedly reflected and if minimum distance between sound sources and reflecting surface is more than 17.2 m, then we hear echoes.
(ii) If the reverberation time in a big hall is too long, then sound becomes distorted, blurred and confusing.