Question

The energy required to excite an electron from $n=2$ to $n=3$ energy state is $47.2eV$. The charge number of the nucleus, around which the electron revolving will be

• A. $5$
• B. $10$
• C. $15$
• D. $20$

Answer 1

The correct option is A $5$

Energy needed $=13.6z^2(\frac{1}{n{{}_1}^2}-\frac{1}{n{{}_2}^2})eV\left[\begin{array}{cc}\therefore from& n_1=2\\ to& n_2=3\end{array}\right]$
$\Rightarrow 47.2=13.6z^2(\frac{1}{4}-\frac{1}{9})$
$\Rightarrow z^2=25$

$\Rightarrow z=5$