Consider the hypothetical situation where the azimuthal quantum number, l, takes values 0 , 1,2, n+1, where n is the principal quantum number. Then, the element with atomic number

Consider the hypothetical situation where the azimuthal quantum n…

MCQ

Consider the hypothetical situation where the azimuthal quantum number, $l$, takes values $0$ , $1,2, \ldots \ldots n+1,$ where $n$ is the principal quantum number. Then, the element with atomic number

A
$13$ has a half$-$filled valence subshell
B
$9$ is the first alkali metal
✓
$8$ is the first noble gas
D
$6$ has a $2 p-$ valence subshell

✓

Answer

Correct option: C.

$8$ is the first noble gas

c
$l=0$ to $( n +1)$

$n =1 \quad n =2$

$l=0,1,2 \quad l=0,1,2,3$

$(n+l) \Rightarrow \frac{1 s}{1} \frac{1 p}{2} \frac{1 d}{3} \quad \frac{2 s}{2} \frac{2 p}{3} \frac{2 d}{4} \frac{2 f}{5}$

$n=3$

$l=0,1,2,3,4$

$\frac{3 s }{3} \frac{3 p }{4} \frac{3 d }{5} \frac{3 f }{6} \frac{3 g }{7}$

Now, in order to write electronic configuration, we need to apply $( n +l)$ rule

Energy order : $1 s <1 p <2 s <1 d <2 p <3 s <2 d$

Option 1) $13: 1 s^{2} 1 p^{6} 2 s^{2} 1 d^{3}$ is not half filled

Option 2) $9: \quad 1 s^{2} 1 p^{6} 2 s^{1}$ is the first alkali metal because after losing one electron, it will achieve first noble gas configuration

Option $3)$ $8: \quad 1 s^{2} 1 p^{6}$ is the first noble gas because after $1 p ^{6} e ^{-}$ will

Option $4)$ $6: \quad 1 s ^{2} 1 p ^{4}$ has $1 p$ valence subshell.