(a) A wall reflects light and a mirror also reflects light. What difference is there in the way they reflect light ? (b) Which type of reflection of light leads to the formation of images ?

(a)A mirror has a highly polished surface which is smooth .So it does not distort the light and parallel beam of incident rays of light remain parallel after reflection. (Regular reflection).
A wall is a rough surface so the light is reflected at different angles and directions i.e parallel beam of incident light doesn’t remain parallel after reflection.. (Irregular reflection)
Regular reflection of light from the plane mirror causes the formation of image. When a parallel beam of light is incident on a plane mirror it is reflected back parallely. Due to this property a plane mirror is used to see our image and not a rough surface.
(b) Regular reflection of light leads to the formation of images