Answer
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Work Step by Step
a. The quantum-mechanical theory of the atom agrees with the Bohr model that electrons cannot possess any energy, but must exist in discrete states with specific energy levels. The expression for the energy of an electron in such a state, $-13.6eV/n^2$, is the same as that postulated by the Bohr model.
The quantum-mechanical theory of the atom also agrees that an atom absorbs or emits a single photon when an electron changes from one energy state to a different one.
b. The quantum-mechanical theory of the atom disagrees with the Bohr model about the depiction of electrons. Bohr pictured the electrons circling the nucleus like planets around a star. The quantum-mechanical theory of the atom pictures the electrons as probability clouds surrounding the nucleus that do not have exactly-known positions or momenta.