The first emission line of hydrogen atomic spectrum in the Balmer series appears at:
(R = Rydberg constant)

For the first emission line in the atomic spectrum of hydrogen in the Balmer series 

n ₁=2 and n₂=3;
The wavenumber is given by the expression

$$\begin{gathered} \frac{1}{\lambda }=R{Z}^2\left[\frac{1}{n_1^2}-\frac{1}{n_2^2}\right] \\ =R{1}^2\left[\frac{1}{2_{ }^2}-\frac{1}{3_{ }^2}\right] \\ \lambda =\frac{5R}{36} c{m}^{-1} \end{gathered}$$