Answer
Lyman series.
Work Step by Step
The transition was from $n=2$ down to $n=1$ so it's in the Lyman series.
The Balmer series of wavelengths are jumps up from $n = 2$ (absorption) or down to $n = 2$ (emission).
The Paschen series of wavelengths are jumps up from $n = 3$ (absorption) or down to $n = 3$ (emission)
