Solution:

Rectilinear propagation describes the tendency of Electromagnetic waves to travel in a straight line.
Light only deviates from a straight line when the medium it is travelling through changes density. This is called refraction.
Reflection- the throwing back by a body or surface of light, heat, or sound without absorbing it.
Diffraction- the process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the wave forms produced.