What is near-sightedness?

$(a)$ Explain the following terms used in relation to defects of vision and corrections provided for them:
$(i)$ Myopia $(ii)$ Astigmatism $(iii)$ Bifocal lenses $(iv)$ Far-sightedness (Hypermetropia).
$(b)$ Describe with a ray diagram how a person with myopia can be helped by spectacles.

When white light is incident on a yellow pigment,which colors of light are reflected?

$A$ near-sighted person can see only nearer objects.

Name the two phenomena involved in the formation of a rainbow.

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