Consider the hypothetical situation where the azimuthal quantum number,
Question:

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

1. 9 is the first alkali metal

2. 13 has a half-filled valence subshell

3. 8 is the first noble gas

4. 6 has a $2 p$-valence subshell

Correct Option: , 2

Solution:

Under the given situation for

$n=1, l=0,1,2$

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

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

According to $(n+l)$ rule of order of filling of subshells will be :

$1 s 1 p 1 d 2 s 2 p 3 s 2 d 3 f$

Atomic number 6 $1 s^{2} 1 p^{4}$

Atomic number 9$1 s^{2} 1 p^{6} 1 d^{1}$

Atomic number 8 $1 s^{2} 1 p^{6}$

Atomic number 13 $1 s^{2} 1 p^{6} 1 d^{5}$

Therefore option (b) is correct. Atomic number of first noble gas will be $18\left(1 s^{2} 1 p^{6} 1 d^{10}\right)$.