Question

How many electrons in an atom may have the following quantum numbers:

$n=4,m_s=-\frac{1}{2}$?

• A. 14
• B. 16
• C. 32
• D. 20

Answer 1

The correct option is B 16

The Maximum no of electrons in 4th energy level $=2\times n^2=2\times 4^2=32$ electrons

In 32 electrons half the electrons have $m_s=-\frac{1}{2}$ and the other have $m_s=+\frac{1}{2}$

So total no of electrons having n = 4 and $m_s=-\frac{1}{2}$ is $\frac{1}{2}\times 32=16$

Hence, the correct option is $\text{B}$