Which optical phenomenon is responsible for the formation of a rainbow?

Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also,indicate the order of the colours of the spectrum obtained.

What is the least distance of distinct vision of a normal human eye (in $cm$)?

$(a)$ Explain why the colour of a clear sky appears blue during the day with the help of a diagram.
$(b)$ Explain why the Sun looks reddish at the time of sunrise and sunset.

With the help of scattering of light,explain the reason for the difference in colours of the Sun as it appears during sunrise/sunset and noon.

$A$ person is able to see objects clearly only when these are lying at distances between $50\, cm$ and $300\, cm$ from his eye.
$(a)$ What kind of defect of vision is he suffering from?
$(b)$ What kind of lenses will be required to increase his range of vision from $25\, cm$ to infinity? Explain.