The Bohr’s model of atom consisted a positively charged nucleus in the center of the atom and electron revolving in the discrete orbits or shells which are concentric and have specific number of electrons in it.

The first shell or orbit nearest to the nucleus was numbered as 1 and named K similarly the rest of shells were named and numbered.

Like n = 1, 2, 3…… ; K, L, M, N,……..

Where n is the shell number.

For Bohr’s model with 4 shells, the electrons no. are as follows:

First shell: 2 electrons

Second shell: 8 electrons

Third shell: 18 electrons

Fourth shell: 18 electrons

But maximum electrons in any shell can only be 8 due to octet rule.