. Read the passage given below and answer the following questions. (3) After the rejection of Rutherford's model of an atom, Neils Bohr put forward his model of atom which was widely accepted. He put forward certain postulates about the model of the atom which are as follows: • Only certain special orbits, known as discrete orbits of electrons, are allowed inside the atom. • While revolving in discrete orbits, the electrons do not radiate energy. Bohr named these orbits as energy levels. These orbits (or shells) are represented by the letters K, L, M, N,. or the numbers n = 1, 2, 3, 4,.... He also suggested that the maximum number of electrons in a given shell can be calculated as 2n 2 , where ‘n’ represents the orbit number or energy level index, 1,2,3,….
(a) Calculate the maximum number of electrons that can be accommodated in an M shell.
(b) Write the distribution of electrons in a sodium atom.
(c) If K and L shells of an atom are completely filled, calculate the total number of electrons in the atom. 

Solution: 

a) 
The maximum number of electrons which can be accommodated in a shell of an atom = 2n2
Where, n is the number of the shell.
For M shell, n=3 
​​​​​​Maximum number of electrons = 2×3×3 = 18 electrons

(b) Sodium atoms has 11 electrons, the distribution of electrons is as follows- 2,8,1

(c) K shell can accommodate 2 electrons and L shell can accommodate 8 electrons, so total of 10 electrons will be present in the atoms.

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