What is a photon?

A photon is indeed defined as a packet of light energy. In the realm of physics, particularly in quantum mechanics, photons are considered the fundamental particles that make up light. Each photon carries a specific amount of energy which is directly related to its frequency, as described by the equation (E = hf), where (E) is energy, (h) is Planck's constant, and (f) is the frequency of the light. Photons have properties of both particles and waves, exhibiting wave-particle duality, but they are fundamentally massless particles that travel at the speed of light in a vacuum.

The other options do not accurately represent the definition of a photon. Waves in the ocean refer to mechanical waves, which have different properties and are not related to the quantum nature of light. A subatomic particle with mass would imply characteristics similar to protons or neutrons, which are not applicable to photons as they have no mass. Lastly, while forces can act on charged particles, photons themselves do not represent a force; rather, they can be carriers of electromagnetic force. This makes the packet of light energy definition the correct and most appropriate characterization of a photon.