Final answer:
Option (D), Planck's finding that energy is lost in discrete quanta led to the quantum hypothesis, which is a cornerstone of quantum mechanics and deviates from classical physics.
Step-by-step explanation:
Max Planck discovered that the energy of a hot body is lost in discrete units rather than continuously, a fundamental observation that gave rise to the field of quantum mechanics. Planck's hypothesis, also known as the quantum hypothesis, states that the energy absorbed or emitted by an object is proportional to the frequency of radiation, with the formula E = hv. This concept was a significant departure from classical physics and contributed to our understanding of processes such as the photoelectric effect, later explained by Einstein using Planck's theory of quanta, which are particles of light now called photons.