Answer: visible region.
- A visible region
- B ultraviolet region
- C infrared region
- D X-ray region
Correct answer: A. visible region
Explanation: Transitions to n = 2 (Balmer series) produce lines in the visible region.

The Geiger–Marsden alpha-scattering result: a few alpha particles bounce back at large angles, which rules out Thomson’s diffuse model and demands a tiny, massive, positively charged nucleus. Image: Kurzon, CC BY 3.0, via Wikimedia Commons.
Concept context
Thomson's plum-pudding model, Rutherford's nuclear model from alpha-scattering, Bohr's postulates and hydrogen spectrum, spectral series (Lyman to Pfund), Rydberg formula, and limitations of each model.