Which of the following phenomena is $NOT$ involved in the formation of a rainbow?

Which part of the eye helps in changing the focal length of the eye lens to focus the image of objects lying at varying distances from the eye?

Which optical phenomenon is responsible for the early sunrise and delayed sunset?

Name the component of white light that deviates the least and the most while passing through a prism.

Study the diagram given below and answer the questions that follow it.
$(i)$ Identify the defect of vision represented in this case. Give a reason for your answer.
$(ii)$ Mention the two causes of this defect.

$A$ person cannot read a book at distances less than $50\, cm$. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams to show the image formation
$(i)$ by defective eye and
$(ii)$ after using corrective lens.