Which color is produced by mixing blue and red?

$A$ person is able to see objects clearly only when these are lying at distances between $50\, cm$ and $300\, cm$ from his eye.
$(a)$ What kind of defect of vision is he suffering from?
$(b)$ What kind of lenses will be required to increase his range of vision from $25\, cm$ to infinity? Explain.

What is Presbyopia?

What color does the region appear when red,green,and blue light overlap?

The figure below shows the refraction of a ray through a prism. Copy the diagram and,ignoring dispersion at the faces $AB$ and $AC$,mark the following angles: $(i)$ The angle of incidence,$(ii)$ the angle of refraction at the face $AB$,$(iii)$ the angle of emergence,and $(iv)$ the angle of deviation.

What is the complementary color of green?