Question

How many spectral lines are observed in spectra of $H{e}^{+}$ ion?

• A. $2$
• B. $4$
• C. $6$
• D. $8$

Answer 1

The correct option is C $6$

Energy levels of helium are: $-54.4eV,-13.6eV,-6.04eV$ and so on.
Given, helium ion electron is in excited state.

Occurrence of spectral lines is possible only if it is in $n=2$, when given $10.2eV$, because if the electron is in any other level, atom ionizes.
$E_4=-3.4eV$
Therefore, electron excites into $n=4$.
No. of emission lines is $\frac{4\times 3}{2}=6$