Question

The electron should be filled in the orbital in accordance with increasing order of their energy. This statement is related with:
A. Aufbau principle
B. Pauli’s principle
C. Hund’s rule
D. Planck’s rule

Answer 1

An orbital is the empty space in the atom where there is the highest or maximum probability of finding an electron. In the atom, there are various energy levels where the electrons are distributed from lower energy level to higher energy level and each orbital can accommodate a maximum of two electrons.

Complete answer:
Let us discuss each rule or principle individually to find out which one proposed the revolutionary idea of filling of electrons in the increasing order of energy level.
(i) Aufbau principle: The aufbau principle, also called the aufbau rule, states that in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. For example, the $1s$ subshell is filled before the $2s$ subshell is occupied. In this way, the electrons of an atom or ion form the most stable electron configuration possible.
(ii) Pauli’s principle: Pauli's Exclusion Principle states that no two electrons in the same atom can have identical values for all four of their quantum numbers. In other words, no more than two electrons can occupy the same orbital and two electrons in the same orbital must have opposite spins.
(iii) Hund’s rule: Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.
(iv) Planck’s rule: According to Planck's rule, different atoms and molecules can emit or absorb energy in discrete quantities only. The smallest amount of energy that can be emitted or absorbed in the form of electromagnetic radiation is known as quantum.

Thus, the correct option is A. Aufbau principle.

Note:
In cases where $(n\; + \;l)$ is the same for two orbitals (e.g., $2p$ and $3s$ ), the ($n\; + \;l$ ) rule says that the orbital with lower $n$ has lower energy. In other words, the size of the orbital has a larger effect on orbital energy than the number of planar nodes.