Question

Maximum number of electrons that can be present in M and N shells respectively are:
(A)$18,32$
(B) $8,18$
(C) $32,50$
(D) $32,18$

Answer 1

Quantum numbers are used to describe the movement of electrons in an atom. Also the shells are represented by the principal quantum number. The electrons present in a shell are the square of principal quantum numbers .

Complete step-by-step answer: In an atom the electrons surround the nucleus in different energy levels. The nucleus is surrounded by orbits having electrons which are known as electron shells. These are known as either first, second or third energy levels or K,L,M energy levels .K shell is the first energy level and can have a maximum of two electrons.
Then the shell closest to the nucleus is the K shell . The number of electrons present in n shells
$= 2{n^2}$
For M shell,
$n = 3$
Number of electrons=$2 \times {(3)^2} = 2 \times 9 = 18$
Similarly for N shell,
$n = 4$
Number of electrons$= 2 \times {(4)^2} = 2 \times 16 = 32$
Hence the number of electrons in M and N shells are $18$ and $32$ respectively.

Therefore the correct answer is option (A).

Note: The above observations are based on three rules that are pauli exclusion principle, hund's rule and aufbau principle. K shell has a maximum of two electrons.