Question

The radiation corresponding to the transitions of electrons from $n=2$ to $n=1$ of hydrogen atoms, fall on $He^{+}$ ions which are in $n=1$ and $n=2$ states. The possible transition of helium ions as they absorb energy from the radiation is

• A. $n=2 \rightarrow n=3$
• B. $n=1 \rightarrow n=4$
• C. $n=2 \rightarrow n=5$
• D. $n=2 \rightarrow n=4$

Answer 1

Answer: (D)

$E=13.6\times 1\times \left(\frac{1}{1^{2}} - \frac{1}{2^{2}}\right)=10.2eV$
For $He^{+}$ in $n=2$ ,
$10.2eV=13.6\times 4\left(\frac{1}{2^{2}} - \frac{1}{n^{2}}\right)$
$\Rightarrow n=4$