How can you identify the type of vision defect a person is suffering from by physically touching their spectacles?

The eye defect known as $Presbyopia$ is corrected by using a $........$ lens.

What is the method of obtaining various colors by mixing primary colors in appropriate proportions called?

$A$ 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

Light rays entering the eye are refracted by the lens and form an image on a specific part of the eye. What is this part called?

What would have been the colour of the earth's sky if there were no atmosphere?