Which part of the eye is responsible for adjusting the size of the pupil?

$(a)$ What will be the colour of the sky in the absence of an atmosphere?
$(b)$ Why are traffic light signals (or danger signals) of red colour?

Identify the phenomena of light involved in the formation of a rainbow.

Short-sightedness (myopia) is caused due to the elongation of the eyeball.

$A$ student sitting on the last bench can read the letters written on the blackboard but is not able to read the letters written in his textbook. Which of the following statements is correct?

Draw ray diagrams each showing $(i)$ myopic eye and $(ii)$ hypermetropic eye.