Ncert Exercises & Solutions

Match the ensuing rules with the corresponding statements:

Rules	Statements
A. Hund’s Rule	1. No two electrons in an atom can have the same set of four quantum numbers.
B. Aufbau Principle	2. Half-filled and completely filled orbitals have extra stability.
C. Pauli's Exclusion Principle	3. Pairing of electrons in the orbitals belonging to the same subshell does not take place until each orbital is singly occupied.
D. Heisenberg’s Uncertainty Principle	4. It is impossible to determine the exact position and exact momentum of a subatomic particle simultaneously.
	5. In the ground state of atoms, orbitals are filled in the order of their increasing energies.

	A	B	C	D
1.	3	5	1	2
2.	1	2	3	4
3.	3	5	1	4
4.	4	5	3	2

Hint: Heisenberg’s Uncertainty Principle states that it is impossible to determine the exact position and exact momentum of a subatomic particle simultaneously.

Explanation:

A. Hund's rule states that pairing of electrons in the orbitals belonging to the same subshell (p, d or f) does not take place until each orbital belonging to that subshell has one electron each i.e., it is singly occupied.

B. Aufbau principle states that in the ground state of the atoms, the orbitals are filled in order of their increasing energies.

C. According to the Pauli exclusion principle, no two electrons in an atom can have the same set of four quantum numbers.

D. Heisenberg's uncertainty principle states that it is impossible to determine the exact position and exact momentum of a subatomic particle simultaneously.

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