In the transition from a higher electron energy level to a lower one, say $m\mapsto n$, a hydrogen atom emits a photon of wavelength $\lambda$ satisfying
$$\frac{1}{\lambda} = R_\infty\left[\frac{1}{n^2}-\frac{1}{m^2}\right]\text{,}$$
where $R_\infty = 1.09737315685\,\mathrm{m}^{-1}$ is the Rydberg constant. For $n=1$, i.e. the destination energy level is the ground state, varying $m$ forms the Lyman series: $\text{Ly}_\alpha$ ($2\mapsto 1$), $\text{Ly}_\beta$ ($3\mapsto 1$), $\text{Ly}_\gamma$ ($4\mapsto 1$), etc. The $n=2$ destination energy level forms the Balmer series: $\text{Ba}_\alpha$ ($3\mapsto 2$), $\text{Ba}_\beta$ ($5\mapsto 2$), etc., which was actually the first series to be discovered, and is frequently labeled simply with hydrogen instead.
What all can be interpreted from this? Is it because, energy of the radiation contained by the flare lies around this wavelength? And why chromosphere ?
A solar flare is a very hot, violent event that radiates energy across the electromagnetic spectrum. The importance of the H-α line is due to the conveniences of observation.
The spectral lines of hydrogen are outside the visible band except for the first four of the Balmer series, from the red H-α line to the violet H-δ line. When an hydrogen ion and an electron recombine into an atom, the result is generally a hydrogen atom in an excited state. Eventually, it decays to the ground state, but it doesn't have to transition directly there, and typically does so in a random sequence of transitions. A very sizable fraction of those transitions, however, include the $3\mapsto 2$ jump that produces the H-α line.
Thus, the presence of the H-α line is an easy way to identify ionized hydrogen, and in particular, a sudden brightening of the H-α line in an emission-line spectrum is an indicator that something energetic is happening to ionize the hydrogen (moreso than usual, that is). And that's where the chromosphere, the low-density "atmosphere" surrounding the Sun, comes in: it has an emission-line spectrum, i.e., its spectrum is bright in narrow bands that correspond to its atomic or molecular composition. This is unlike the photosphere, which has an absorption-line spectrum instead.