Which of the following best describes a photon?

A photon is best described as an elementary particle of light or electromagnetic radiation. This definition captures its fundamental role in quantum physics, where photons are considered the basic units that carry electromagnetic force. They are massless particles that move at the speed of light and exhibit both wave-like and particle-like properties, a duality that is central to quantum mechanics.

Photons are responsible for the transmission of light and other forms of electromagnetic radiation, ranging from radio waves to gamma rays. This is significant in understanding how energy moves through space and how electromagnetic interactions take place.

The other options do not accurately characterize a photon: for example, while some particles carry electric charge, photons do not have any charge. The notion of a gaseous substance does not apply to photons as they are not made up of atoms or molecules. Additionally, while photons do exhibit wave characteristics, the description of a waveform in a vacuum is overly simplistic and does not acknowledge the particle nature of a photon. Thus, identifying a photon as an elementary particle of light encapsulates its properties and role in physics succinctly and effectively.