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In a hydrogen atom, the orbital radius of an electron changes from 2.12 Angstrom to 4.77 Angstrom. Which of the following correctly describes the energy transition that occurred?

1. The atom absorbed a photon carrying 1.51 eV of energy
2. The atom absorbed a photon carrying 1.89 eV of energy
3. The atom emitted a photon carrying 10.2 eV of energy
4. The atom emitted a photon carrying 1.04 eV of energy

Correct answer: The atom absorbed a photon carrying 1.89 eV of energy

Solution

r = 2.12 Angstrom corresponds to n=2 and r = 4.77 Angstrom corresponds to n=3. Since the radius increased, the electron moved to a higher level, so a photon was absorbed with energy E3 - E2 = (-1.51) - (-3.4) = 1.89 eV.

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