What do we call the distance between two consecutive compressions of a sound wave?

What is the phenomenon where sound waves bounce off a surface called?

How much should minimum distance be between the source of sound and reflecting surface, so that an echo can be heard clearly?

What is the name of the part of the ear that collects sound waves?

Which one of the following cannot be the unit of frequency of a sound wave?

What is the name of the device used to convert sound waves into electrical signals?