Question

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 :

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

Answer 1

Answer: (A)

Under the given situation for
$<br/>\begin{array}{l}<br/>n=1,l=0,1,2\\ <br/>n=2,l=0,1,2,3\\ <br/>n=3,l=0,1,2,3,4<br/>\end{array}<br/>$
According to $(n+l)$ rule of order of filling of subshells will be :
$1s1p1d2s2p3s2d3f$
Atomic number $61s^{2}1p^4$
Atomic number $91s^{2}1p^{6}1d^1$
Atomic number $81s^{2}1p^6$
Atomic number $131s^{2}1p^{6}1d^5$
Therefore option (b) is correct. Atomic number of first noble gas will be $18\left(1s^{2}1p^{6}1d^{10}\right)$.