The correct answer is B. Spontaneous emission.
Spontaneous emission is the process by which an excited atom or molecule emits a photon without any external stimulus. The photon is emitted when the atom or molecule decays from a higher energy state to a lower energy state. The energy of the photon is equal to the difference in energy between the two states.
Blackbody radiation is the electromagnetic radiation emitted by a black body, an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation is characterized by a continuous spectrum that peaks at a wavelength that depends on the temperature of the black body.
Synchrotron radiation is electromagnetic radiation produced by charged particles moving in a curved path. The radiation is emitted because the particles accelerate as they move around the curve. The amount of radiation emitted depends on the energy of the particles, the radius of the curve, and the mass of the particles.
Planck’s oscillation is a physical phenomenon in which a particle oscillates at a frequency that is determined by its mass and the force acting on it. The oscillation can be either classical or quantum mechanical. In classical mechanics, the particle oscillates at a frequency that is determined by its mass and the restoring force. In quantum mechanics, the particle oscillates at a frequency that is determined by its mass and the Planck constant.