Concept: When excited hydrogen electrons fall back to lower energy levels, they emit photons. The destination level dictates the energy (and thus the spectrum band) of the emitted light.
Formula: $$ E = h\nu $$
Solution: - Lyman series: Electrons fall to \( n=1 \). The energy gap is massive, emitting high-energy ultraviolet (UV) light.
- Balmer series: Electrons fall to \( n=2 \). The energy gap matches the energy of visible light photons. The lines appear as specific colors (red, green, blue-violet) visible to the human eye.
- Paschen, Brackett, and Pfund series: Electrons fall to \( n=3, 4, 5 \) respectively. These gaps are very small, emitting low-energy infrared (IR) light.
Why other options are incorrect: Paschen and Pfund are strictly in the invisible infrared region. Lyman is strictly in the invisible ultraviolet region.
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