Final answer:
The correct answer is A) Quantum Theory, which describes the emission of energy from a hot body in discrete units. This concept is crucial in understanding blackbody radiation and the foundation of quantum mechanics.
Step-by-step explanation:
The energy of a hot body is emitted in discrete units as described by the concept of quantum theory. This phenomenon is a foundational principle in quantum mechanics and is particularly exemplified in the study of blackbody radiation. A blackbody is an idealized physical body that absorbs all incident electromagnetic radiation and re-emits energy at a characteristic spectrum that depends on its temperature. This emission of radiation, rather than being continuous, occurs in packets of energy known as quanta, proportional to the frequency of the radiation (E = hv, where h is Planck's constant and v is the frequency).
Max Planck's explanation for this quantization of energy resolved the 'ultraviolet catastrophe' and led to the development of quantum mechanics, which significantly influenced modern science and technology. Furthermore, Niels Bohr's incorporation of this quantum concept into his model of the atom explained the observed discrete emission spectra, further validating the quantum description of energy emission.
The correct answer is A) Quantum Theory.