Which of the following are the primary colours of light?

When red and green light overlap,what color does that region appear?

What color of light is produced when blue and yellow light are superimposed?

What are the colors obtained by mixing primary colors called?

Account for the following:
$(a)$ Part of the human eye that helps in changing the focal length of the eye lens.
$(b)$ The condition resulting due to the eye lens becoming cloudy.
$(c)$ The factors on which the colour of the scattered white light depends.
$(d)$ The range of vision of a normal eye.
$(e)$ The sky appears dark to the astronauts in space.

In an astronomical telescope,how is the focal length of the objective lens compared to the focal length of the eyepiece?