Please help me out 1.Anna could easily hear her echo when she shouted in her school's multipurpose hall. Later she shouted in the same manner in her room at her home but she was not able to hear any echo. Explain.

2.There is an explosion on the surface of a lake and two persons john and Dante hear its sound. John is 150 m away on a boat and Dante is 150 m
below the surface of water. Who would hear the sound first and why?

3.Both sound waves and light waves undergo the phenomenon of refraction
when they travel from air to water. How is refraction of sound waves different
from the refraction of light waves?