Question

10. The Rays other than paraxial rays will be focused at different
points on the principal areas, this phenomenon is known as​

Answer 1

ANSWER

A lens will not focus different colors in exactly the same place because the focal length depends on refraction and the index of refraction for blue light (short wavelengths) is larger than that of red light (long wavelengths). This phenomenon is called chromatic aberration.

The image will be like this:

A circular spot will be formed whose edges are violet and the central portion red.