Choose the correct word/words to complete the following sentence —

When sound travels in a medium ………. (the particles of the medium, the source, the disturbance, the medium) travels in form of a wave.

Name the two kinds of waves in form of which sound travels in a medium.

What is a transverse wave? In which medium: solid, liquid or gas, can it be produced?

Define the term amplitude of a wave. Write it's S.I. unit.