Question

The fine structure of hydrogen spectrum can be explained by:
(A) The presence of neutrons in the nucleus
(B) The finite size of nucleus
(C) The orbital angular momentum of electrons
(D) The spin angular momentum of electrons

Answer 1

Hint
We should know that the emission spectrum of atomic hydrogen has been divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in an atom. Although hydrogen has only one electron, it contains many energy levels. When its electron jumps from higher energy level to a lower one, it releases a photon. Those photons appear as lines. For this reason, though hydrogen has only one electron, more than one emission line is observed in its spectrum. All observed spectral lines are due to electrons moving between energy levels in the atom. The spectral series are important in astronomy for detecting the presence of hydrogen and calculating red shifts. Further series for hydrogen as well as other elements were discovered as spectroscopy techniques developed. Based on this concept we have to solve this question.

Complete step by step answer
From the given question, we can deduce that the fine structure of the hydrogen spectrum is explained by spin angular momentum of electrons whereas orbital angular momentum, finite size of nucleus or the presence of neutrons in the nucleus does not explain the fine structure of the hydrogen spectrum. Total orbital angular momentum and total spin angular momentum. The total spin momentum has magnitude Square root of $ \sqrt{S\left( S\text{ }+\text{ }1 \right)(\hbar )} $ , in which S is an integer or half an odd integer, depending on whether the number of electrons is even or odd.
Therefore, the correct answer is Option (B).

Note
We should be having an idea that Niels Bohr explained the line spectrum of the hydrogen atom by assuming that the electron moved in circular orbits and that orbits with only certain radii were allowed. The orbit closest to the nucleus represented the ground state of the atom and was most stable; orbits farther away were higher-energy excited states. The dark lines correspond to the frequencies of light that have been absorbed by the gas. As the photons of light are absorbed by electrons, the electrons move into higher energy levels. This is the opposite process of emission. Absorption spectroscopy is performed across the electromagnetic spectrum.