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⚛️ Physics  ·  Atoms  ·  NEET & JEE

In the Bohr model of hydrogen, the radius of the n = 2 orbit (Bohr radius 0.53 Å) is:

Answer: 2.12 Å.

  • A 0.26 Å
  • B 1.06 Å
  • C 2.12 Å
  • D 0.53 Å

Correct answer: C. 2.12 Å

Explanation: r<sub>n</sub> = n²·a₀ = 4·0.53 = 2.12 Å.

Comparison of the Thomson model and the Rutherford model of the atom: in the Thomson plum pudding model alpha particles pass almost straight through a diffuse positive sphere, while in the Rutherford model a concentrated central nucleus deflects some alpha particles through large angles, with the lower panels showing the alpha particle source and gold foil and the observed result of wide-angle scattering

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.

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