Which of the following colors is not a primary color?

In the eye of a person suffering from myopia (nearsightedness),where is the image of a distant object formed?

$A$ student cannot read properly from the blackboard while sitting on the front desk in a large classroom. However,he can read clearly while sitting on the last desk of the classroom.
$(a)$ Draw ray diagrams to illustrate the formation of the image of the blackboard writing by his eye lens when he is seated at the $(i)$ front desk,$(ii)$ last desk.
$(b)$ Name the defect of the eye from which the student is suffering.
$(c)$ Name the type of lens that would enable him to see the blackboard writing clearly when seated at the front desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.

The far point of a myopic person is $80 \, cm$ in front of the eyes. What is the nature and power of the lens required to enable him to see very distant objects distinctly?

$(a)$ Explain the phenomenon of scattering of light. State the factor on which the colour of scattered light depends.
$(b)$ List any two natural phenomena based on the scattering of light.

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