The correct answer is option 1: Photons.
Light quanta, or particles of light, are known as photons. Photons are fundamental particles that have properties of both particles and waves. They have zero mass and travel at the speed of light in a vacuum.
Option 2: Protons are elementary particles that carry a positive charge and are found in the nucleus of an atom. They are much larger and more massive than photons and are not involved in the propagation of light.
Option 3: Neutrons are neutral particles that are also found in the nucleus of an atom. Like protons, they are much larger and more massive than photons and do not participate in the propagation of light.
Option 4: Electrons are negatively charged particles that orbit the nucleus of an atom. While they are involved in the interaction and absorption of photons, they are not a description of the propagation of light quanta itself.
In conclusion, photons accurately describe the propagation of light quanta due to their unique properties as massless particles that travel at the speed of light.