A photon is

Correct option is A

The correct answer is (a) a quanta of light energy

Explanation:
• According to quantum mechanics and Albert Einstein's theory of the photoelectric effect, a photon represents a discrete packet or quanta of light energy.
• Light travels in the form of these massless energetic particles, and the energy of a single photon is strictly proportional to its frequency ($E = hf$).

Information Booster:
• Photons definitively travel at the speed of light in a vacuum (approximately $3 \times 10^8$ meters per second).
• They exhibit wave-particle duality, meaning they display characteristics of both continuous waves and discrete microscopic particles.

Additional Knowledge:
a quanta of material (substance) (Option b)
• Photons are explicitly massless elementary particles and do not constitute physical matter or "substance" with rest mass.
a positively charged particle (Option c)
• Photons are completely electrically neutral. A positron or a proton would fit the description of a positively charged particle.
a light intensity gauge (Option d)
• A photon is the actual physical particle of light, not an instrument or gauge used for measurement.
None of the above/More than one of the above (Option e)
• Incorrect, as option (a) defines it perfectly.

So the correct answer is (a)