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Answer :

The following rules are followed for writing the number of electrons in different energy levels or shells:

(i) The maximum number of electrons present in a shell is given by the formula \( 2n^2 \) , where ‘n’ is the orbit number or energy level index, 1, 2, 3, ….

Hence the maximum number of electrons in different shells are as follows:

second orbit (n = 2) or L-shell will be = 2 × 2

third orbit (n = 3) or M-shell will be = 2 × 3

fourth orbit (n = 4) or N-shell will be = 2 × 4

(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8 for all shells except for K-shell which can accommodate only 2 electrons .

(iii) Electrons are not accommodated in a given shell, unless the inner shells are filled which means the shells are filled in a step-wise manner.

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