Answer: Niels Bohr.
- A Niels Bohr
- B John Dalton
- C J. J. Thomson
- D Isaac Newton
Correct answer: A. Niels Bohr
Explanation: Bohr proposed the model of quantised electron orbits in 1913.

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.