CBSE Class 9 Answered

The names of electron shells come from a spectroscopist Charles G Barkla, who studied the X rays that are emitted by atoms when they are hit by high energy electrons.He observed that atoms emits two types of X rays.

The energy of these two types of X Rays are different and Barkla originally named higher energy X rays as type A and lower energy X rays as type B. Later Barkla realized that the highest energy X rays produced in experiments are might not be of highest energy X rays. So he wanted to make sure that there should be room to add more discoveries without ending up with alphabetical list of X rays. So he named the innermost shell as K shell.