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Who discovered spin quantum number?
A. Uhlenbeck and Goudsmit
B. Niels Bohr
C. Zeeman
D. Sommerfeld

Last updated date: 20th Mar 2023
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Hint: Each of the above mentioned have discovered and named many theories and concepts, and some of them use their names in the theory itself. With this, you may find the answer to this question.   

Complete answer:
Uhlenbeck and Goudsmit postulated the existence of the property of particles that behaved like an angular momentum. This was proposed to be an intrinsic property which is particular to a given particle. They both discovered electron spin which is related to spin quantum number  while studying about the spectral lines of the zeeman effect. Therefore, option A is the correct one. 

Niels Bohr was involved in the discovery of the electron and radioactivity. These discoveries led to different models being proposed for the atom’s structure. He also proposed a theory for the hydrogen atom. After him, the quantized shell model of the atom – called Bohr Atomic Model – was published which explains how electrons can have stable orbits around the nucleus. With all these points, we can safely rule out option B.

Zeeman studied how light was affected by magnetic fields. He found out that under the influence of magnetic fields, the lines in a spectrum split up into several lines. He also found that when an element is burned in a flame to produce a spectrum, that is also subject to the influence of a magnetic field. Eventually, he named this phenomenon the Zeeman effect. 

Sommerfeld was one of the pioneers of quantum and atomic physics. He is known for introducing the azimuthal quantum number (2nd quantum number) and the magnetic quantum number (3rd quantum number). He also improved Bohr’s Atomic Model by replacing the originally thought circular orbits with elliptical orbits. Therefore, option D is not the correct answer. 

Therefore, Uhlenbeck and Goudsmit discovered the spin quantum number and hence option (A) is correct.

Note: Such questions are very specific and fact-based. Make sure you learn your chapters thoroughly and take note of such details. Also, by having knowledge of the names of scientists that made big discoveries such as the ones in this question is important and will help you answer such questions.