The wave length of ${\mathrm{H}}_{\mathrm{\delta }}$ line of Balmer series of a hydrogen atom is nearly
$\left(\mathrm{R}=1.08\times {10}^7{\mathrm{m}}^{-1}\right)$

For the alpha line, the first transition is considered.

$$\begin{gathered} \frac{1}{\mathrm{\lambda }}={\mathrm{R}}_{\mathrm{H}}{\mathrm{Z}}^2\left[\frac{1}{{\mathrm{n}}_1^2}-\frac{1}{{\mathrm{n}}_2^2}\right] \\ \frac{1}{\mathrm{\lambda }}=1.08\times {10}^7\times {\left(1\right)}^2\left[\frac{1}{2^2}-\frac{1}{6^2}\right]=\frac{8\mathrm{R}}{36} \\ \mathrm{\lambda }=\frac{36}{8.64\times {10}^7}\times {10}^{10}\cong 4090 \stackrel{°}{\mathrm{A}} \end{gathered}$$