⚛️ Physics · Atoms · NEET & JEE

The number of distinct spectral lines emitted when hydrogen atoms de-excite from the n = 4 level is:

Answer: 6.

A 3
B 4
C 6
D 10

Correct answer: C. 6

Explanation: Number of lines = n(n − 1)/2 = 4·3/2 = 6.

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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The number of distinct spectral lines emitted when hydrogen atoms de-excite from the n = 4 level is:

Concept context

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