When blue and yellow pigments are mixed and white light is incident on the mixture,which color of light is reflected?

What is the central aperture of the eye located behind the cornea called?

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?

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

$(a)$ State two main causes of a person developing near-sightedness. How can this defect be corrected?
$(b)$ What is 'astigmatism' and how is this vision defect corrected?

$A$ prism $ABC$ (with $BC$ as base) is placed in different orientations. $A$ narrow beam of white light is incident on the prism as shown in the figure. In which of the following cases,after dispersion,the third colour from the top corresponds to the colour of the sky?