Which uses the refractive properties of light to separate it into its different wavelengths?
a.
white light from the surface of a mirror
b.
colored light as it travels from a solid medium to a liquid medium
c.
visible light as it passes through a lens
d.
sunlight through droplets of water in the atmosphere

A). No.  A mirror doesn't separate light into its different wavelengths.

B). No.  Light doesn't separate into its different wavelengths when it
goes, say, from glass into water.

C). No.  When light goes through your glasses, it doesn't separate
into its different wavelengths.

D). Yes !  When sunlight shines into droplets of water in the atmosphere,
it comes out separated into its different wavelengths.  When we see that
happening in the air in front of us, we call it a "rainbow".

It's because 3 if it was 10 it wouldn't look right do it goes up to 4d