The one electron of hydrogen  , when excited  , reaches 3rd energy level and degeneracy is determined by (n+l) . where n= energy level  , l= 0 for s , 1 for p , 2 for d, 3 for f

The one electron of hydrogen, when excited, reaches 3rd energy level and degeneracy is determined by $(n + l)$, where $n$ - energy level, $l = 0$ for $\mathrm{s}$, $1$ for $\mathrm{p}$, $2$ for $\mathrm{d}$, $3$ for $\mathrm{f}$.