Which optical phenomenon is responsible for the twinkling of stars?

$A$ person has to use a concave lens in his spectacles. Which defect of vision is he suffering from?

Draw a ray diagram showing the refraction of light through a glass prism and mark the following:
$(a)$ Incident ray
$(b)$ Emergent ray
$(c)$ Refracted ray
$(d)$ Angle of incidence
$(e)$ Angle of deviation
$(f)$ Angle of emergence

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

How are we able to see nearby and also the distant objects clearly?

What is meant by the far point?