Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset?

$A$ $14$ year old student is not able to see clearly the questions written on the blackboard placed at a distance of $5\, m$ from him.
$(a)$ Name the defect of vision he is suffering from.
$(b)$ With the help of labelled ray diagrams show how this defect can be corrected.
$(c)$ Name the type of lens used to correct this defect.

Light coming from the sun is white light and contains seven colours.

Which color of light undergoes the least scattering due to the atmosphere?

The brilliance of a diamond is due to which phenomenon?

Which of the following is not a secondary color?