Question

The maximum number of electrons that can have principal quantum number, n = 3 and spin quantum number, $m_s=-\frac{1}{2}$ is:

• A. 6
• B. 7
• C. 8
• D. 9

Answer 1

The correct option is D 9

For a shell with principal quantum number 'n', maximum number of electrons that can occupy the shell = $2n^2$

For n = 3, maximum number of electrons = $2\times 3^2$ = 18

Half of them will have $m_s=-\frac{1}{2}$ and the other half will have $m_s=+\frac{1}{2}$ .

$\therefore$ Maximum number of electrons with $m_s=-\frac{1}{2}$ and n = 3 is $\frac{18}{2}$ or 9.