• # question_answer Beryllium fourth electron will have the four quantum numbers :- A) n - 1 $\ell$- 0 m - 0 s - $1/2$ B) n - 1 $\ell$- 1 m - 1 s - $1/2$ C) n - 2 $\ell$- 0 m - 0 s - $-1/2$ D) n - 2 $\ell$- 1 m - 0 s - $+1/2$

$_{4}Be\Rightarrow 1{{s}^{2}}2{{s}^{2}}$ $\Rightarrow$ $n=2,\,\ell =0,\,m=0,\,s=+\frac{1}{2}$  or $-\frac{1}{2}$