Name the outermost layer of the eye. What is its function?

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.

To correct astigmatism,we use a cylindrical lens.

$A$ student finds the writing on the blackboard blurred and unclear while sitting on the last desk in a classroom. He,however,sees it clearly while sitting on the front desk at about $2\, m$ from the blackboard.
$(a)$ Draw ray diagrams to illustrate the formation of image of the blackboard writing by his eye lens when he is seated at the $(i)$ last desk,$(ii)$ front desk.
$(b)$ Name the defect of the eye from which the student is suffering.
$(c)$ Name the kind of lens that would help him to see clearly even when he is seated at the last desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.

What is the difference in the colours of the Sun observed during sunrise/sunset and at noon? Provide an explanation for each.

$A$ beam of white light falling on a glass prism gets split up into seven colours marked $1$ to $7$ as shown in the diagram.
$(a)$ The colours at positions marked $3$ and $5$ are similar to the colour of the sky and the colour of gold metal respectively. Is the above statement made by the student correct or incorrect? Justify.
$(b)$ Which of the above shown positions corresponds approximately to the colour of:
$(i)$ a brinjal
$(ii)$ danger signal
$(iii)$ neel (indigo) which is applied to clothes
$(iv)$ orange