There is no answer that is right except for C. Natural Selection.
Genetic Recombination doesn't change gene frequency;nor does migration. (Unless it's local)
Mutation could be the answer, but since mutations are too rare to really power Evolution, the only logical answer is Natural Selection.
Explanation:
Bohr model is able to explain the electromagnetic spectrum produced by different atoms of different elements. This is because an electron around the nucleus of an atom occupies distinct orbital levels around the nucleus and not in between. When an electron absorbs a specific wavelength of electromagnetic spectrum it 'hops' to an upper electron energy level equivalent to this wavelength of radiation. When the atom 'hops' to a lower orbital level it releases ta specific wavelength of radiation that is equivalent to the difference in the energy levels. This was unaccounted for in the Rutherford's planetary model.
The electron cloud model is thought to be an improvement on the Bohr model because it accounts for the Heisenberg Uncertainty Principle which stipulates that it is impossible to ascertain the momentum and location of an electron at the same time (because merely viewing an electron using light -or any kind of radiation - will change its direction and velocity). This model explains the likely position of an electron using probabilistic equations. The electron cloud model can therefore be used to explain bonding between atoms.
Learn More:
For more on atomic theories check out;
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The answer is most definitely a
