Question

Electronic configuration of magnesium is:
A.2,8,2
B.2,8, 1
C.2,8,7
D.2,1

Answer 1

Hint: The electronic configuration of any element is written in the order of increasing energies of the principal shells . Before writing electronic configuration of any element we should know its atomic number which is equal to the number of electrons present in the atom .

Complete step by step answer:
Electronic configuration of an element is the distribution of electrons in different shells, subshells and orbitals of the atom.
The shells in which the electrons are arranged are named as K,L,M,N and so on
starting from the inner shell to the valence shell magnesium atom has 3 shells in it.
The atomic no. of magnesium is 12 and we know that the atomic number is the total number of electrons present in the atom.
Also, the shells of the atom can accommodate only a certain number of electrons which is governed by the $2n^2$ rule.
where , n =number of shell
that is , in the K shell , $$2\times 1^2=2$$ which means the K shell can accommodate a maximum of 2 electrons.
in the L shell , $2\times 2^2=8$ , L shell can accommodate a maximum of 8 electrons.
Similarly , the M shell can accommodate a maximum of 18 electrons and so on.
So, the distribution of 12 electrons in the magnesium atom is :
2 in the first shell ,8 in the second shell and the rest 2 electrons in the valence shell such that the electronic configuration becomes 2,8,2 .

So, the correct answer is Option A .

Note:
The filling of electrons takes place according to the Aufbau principle which states that the orbitals are filled in order of their increasing energies , that is the higher energy levels are filled only when the lower energy levels are fully filled .