The correct answer of 4 is
both assertion and reason are true and reason is the correct explanation of assertion.
The correct answer of 5 is
Convex mirror are used as rear view mirror in vehicles because it gives wider field of view. The field view of a convex mirror is large and it forms a diminished image so that the vehicles coming from behind can be observed. So, A and R are correct, and R is the correct explanation of A.