Question

Define shells.

Answer 1

An atom is made up of two parts:

1. Nucleus: The nucleus is the central part of the atom which contains protons and neutrons.
2. Shells: The shells are the circular paths or orbits around the nucleus in which electrons revolve. Shells can be named as K, L,M, N etc.

Thus,

Shells are the circular paths or orbits around the nucleus in which electrons revolve.