Question

Assertion : The maximum number of electrons in the shell with principal quantum number $n$ is equal to $2n^2$.
Reason : Two electrons can have the same value of three quantum numbers $n,l$ and $m_b$ but must have the opposite spin quantum number.

• A. If both assertion and reason are true and reason is the correct explanation of assertion.
• B. If both assertion and reason are true but reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both assertion and reason are false.

Answer 1

Answer: (A)

In $n^{\text{th }}$ shell, the total number of orbitals are $n^2$ where each orbital can occupy a maximum of two electrons with opposite spin quantum number as $+1/2$ and $-1/2$.
Rest of the three quantum numbers in a given orbital will be same.
Thus it will follow Pauli's exclusion principle.
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion