Question

REFER TO THE ELECTRON CONFIGURATIONS SHOWN BELOW.
(A)1s2 2s2 2p6 3s2 3p4
(B)1s2 2s2 2p6 3s2 3p6 4s1 3d5
(C)1s2 2s2 2p8 3s2 3p6
(D)1s2 2s2 2p6 3s2 3p6 4s2 3d4
(E)1s2 2s2 2p6 3s2 3p6
5 -electron configuration of Cr
6 -violates Pauli exclusion principle
7 -noble gas configuration

with explaniation

Answer 1

According to the condition given in question,

5) The electronic configuration of chromium is (B)1s2 2s2 2p6 3s2 3p6 4s1 3d5 (option B)

6) Paulis exclusion principle states that no two electrons will have the all four quantum numbers the same.
further it states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons
we all know that a P orbital can hold a maximum of 6 electrons in its valency shell.
But in option C, the P orbital is having 8 electrons which is impossible
and hence (C)1s2 2s2 2p8 3s2 3p6 violates paulis exclusion principle.

7) A noble gas electron configuration is a configuration that completes the Octet Rule of achieving 8 valence electrons in its outermost shell. so from the options given, (E)1s2 2s2 2p6 3s2 3p6 has noble gas coniguration because it has fulfilled outer most shell.