Which part of the eye controls the amount of light entering it?

$A$ glass slab is placed over a page on which the word $VIBGYOR$ is printed with each letter in its corresponding colour. $(i)$ Will the image of all the letters be in the same place? $(ii)$ If not, state which letter will be raised to the maximum. Give a reason for your answer.

$A$ prism causes dispersion of white light while a rectangular glass block does not. Explain.

When white light is incident on a yellow pigment,which color of light is not reflected?

How is the sense of vision carried from the eye to the brain?

Which of the following are the primary colours of light?