Answer: 13.6 eV.
- A 1.51 eV
- B 3.4 eV
- C 13.6 eV
- D 27.2 eV
Correct answer: C. 13.6 eV
Explanation: The energy needed to remove the electron from n = 1 is 13.6 eV.

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.