Question

Assertion :The configuration of $B$-atom cannot be $1s^{2}2s^2$. Reason: Hund's rule demands that the configuration should display maximum multiplicity.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Both Assertion and Reason are incorrect.

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

The configuration of B-atom cannot be $1s^{2}2s^2$ as B atom has 5 electrons. So it's configuration will be $1s^{2}2s^{2}2p^1$.
Hund's rule demands that the configuration should display maximum multiplicity.
For example, The electronic configuration of N is $1s^{2}2s^{2}2p_x^{1}2p_y^{1}2p_z^1$ and not $1s^{2}2s^{2}2p_x^{2}2p_y^{1}2p_z^0$
The electronic configuration of the ground state of an atom is the one which has the greatest multiplicity.
This is according to Hund's rule of maximum multiplicity.
"When several orbitals of equal energy (degenerate orbitals) are available, the electrons first fill all the orbitals singly before pairing in any of these orbitals".