Number of spectral lines obtained in He ^ + spectra, when an...

The formula used here is:

Number of spectral lines $= \mathop{∑}_{}^{}\left({n}_{2} - {n}_{1}\right)$

${n}_{2}$= Highest energy level=6(fifth excited state)

${n}_{1}$=Lowest energy level=2(first excited state)

Number of spectral lines

$= \mathop{∑}_{}^{}\left(6 - 2\right) = 10$

Number of spectral lines in ${He}^{+}$ for transition from $n = 6$ to $n = 2$ are $10$