The Bohr model of the atom addressed the problem of why electrons didn't fall into the positive nucleus.
In atomic physics, the Rutherford–Bohr model or Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces.
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The Bohr model of atom addressed the problem of why electrons did not fall into the positive nucleus.
As per Rutherford's atomic model, electrons are revolving around the nucleus just like planets are revolving around the sun. But his description about electronic motion was against the Clark Maxwell's electromagnetic theory .
As per Maxwell any charged particle under accelerated motion will release energy. The electron is a negatively charged particle which under acceleration will come closer and closer to the nucleus and finally it will fall on the nucleus for which the whole atom will be destroyed. The path of electron will be a spiral one instead of circular. Hence Rutherford's theory could not explain the stability of nucleus.
Bohr addressed that electron in particular orbit has a fixed amount of energy .There will be no emission or absorption of energy as long as electron revolves around the nucleus.The electron will absorb energy when it will jump from ground state to excited state and will emit energy when it will jump from excited state to ground state.
Hence the option A is right,.