The wavelength of light for the least energetic photons emitted in the Lyman series of the hydrogen spectrum…
The wavelength of light for the least energetic photons emitted in the Lyman series of the hydrogen spectrum is nearly [Take $\mathrm{hc}=1240 \mathrm{eV}-\mathrm{nm}$, change in energy of the levels $=10.2 \mathrm{eV}]$
$150 \mathrm{~nm}$
$122 \mathrm{~nm}$
$102 \mathrm{~nm}$
$82 \mathrm{~nm}$
Solution
For least energetic photon emitted in Lyman series, $E=E_2-E_1=10.2 \mathrm{eV}$
$\begin{aligned}
\lambda=\frac{\mathrm{hc}}{\mathrm{E}} & =\frac{1240}{10.2} \mathrm{~nm} \\
& =121.57 \mathrm{~nm} \approx 122 \mathrm{~nm}
\end{aligned}$