The human eye forms the image of an object at its

Which optical phenomenon is responsible for the formation of a rainbow?

What is the far point of a person with normal vision?

List four common defects of vision that can be corrected with the use of spectacles.

What is meant by scattering of light? Mention the factor on which it depends. Explain why the colour of the clear sky is blue? An astronaut in space finds the sky to be dark. Explain the reason for this observation.

Account for the following:
$(a)$ Part of the human eye that helps in changing the focal length of the eye lens.
$(b)$ The condition resulting due to the eye lens becoming cloudy.
$(c)$ The factors on which the colour of the scattered white light depends.
$(d)$ The range of vision of a normal eye.
$(e)$ The sky appears dark to the astronauts in space.