Why do we have two eyes for vision instead of just one?

What is meant by persistence of vision?

Which color is produced by mixing blue and red?

With the help of a diagram,explain the formation of a rainbow in the sky.

The change in focal length of an eye lens to focus the image of objects at varying distances is done by the action of the

$(i)$ Write the range of distance for a person having normal vision.
$(ii)$ $A$ person needs to use glasses for reading a newspaper. Identify the defect in his vision and the type of lens he would need to correct it.
$(iii)$ Sometimes when we enter into a dark room from bright sunlight,we are unable to see objects clearly. Why?