Question

Which of the following sets of quantum numbers represents the $19^{th}$ electron in chromium? ($Z= 24$ for $Cr$)

• A. $\left(4,1,-1,+\frac{1}{2}\right)$
• B. $\left(4,0,0,+\frac{1}{2}\right)$
• C. $\left(3,2,0,-\frac{1}{2}\right)$
• D. $\left(3,2,-2,+\frac{1}{2}\right)$

Answer 1

Answer: (B)

The ground state electronic configuration of $Cr$ is as
${ }_{24} Cr =[ Ar ] 3 d^{5}, 4 s^{1}$
$\because$ The $19^\text{th}$ electron enters in $4 s^{1}$ subshell.
For $4 s^{1}$
$n=4, l =0$ [For $s$ orbital, $l=0$]
$m =0 [\therefore m=-l \text { to }+l]$
$s =+1 / 2$