Question

Select the correct option according to Hund’s rule and Pauli’s exclusion principle.
I.

II.

III.

IV.

A.Both I and II
B.Both II and III
C.Both I and III
D.Both III and IV

Answer 1

Hint: We must know that the Hund’s Rule states that every orbital in a subshell is first singly occupied by the electron before being occupied by the second electron. Pauli’s exclusion principle, no two electrons have the same set of quantum numbers.

Complete step by step answer:
Let’s start with discussing the Hund’s rule and Pauli’s exclusion principle, Hund’s Rule states that every orbital in a subshell is first singly occupied by the electron before being occupied by the second electron. In easy words, only one electron enters each orbital and after each orbital is having a single electron each, only then the second electron enters the orbitals. According to Pauli’s exclusion principle, no two electrons have the same set of quantum numbers. Means, if there are two electrons in the same subshell; same orbital then their spin will be different.
So, considering both the rules, let’s solve the question.
In I
Both the electrons are present in the 1st orbital in opposite spins, so Pauli’s exclusion principle is valid in this case but Hund’s rule has been violated, which means I. is not a correct option.

In II
There are 4 electrons and they are present in the first two orbitals, Pauli’s exclusion principle is being followed but hund’s rule has been violated, which means II. This is also not a correct option.

In III
There are also 4 electrons and all three orbitals are being used along with 2 electrons in the 1st orbital and one each in the 2nd and 3rd orbital. Clearly, both the Hund’s rule and Pauli’s exclusion principle is being followed. So, III is a correct option.

In IV
There are 5 electrons and all 3 orbitals are being used. Clearly, Hund’s rule and Pauli’s exclusion principle is being followed. So, option IV is also correct.

Hence, the answer to this question is option D. both III and IV.

Note:
We can use both the Hund’s Rule and Pauli’s exclusion principle to understand how the electrons are placed in orbitals and how to place them inside the orbitals. They are also important to understand that each electron in the atom has their own identity, which is known as Pauli’s exclusion principle.