Final answer:
The smallest discrete value of electromagnetic energy is called the photon, which is a quantum of energy and an indivisible particle of light. Energy at the submicroscopic scale can be measured in electron volts (eV).
Step-by-step explanation:
The smallest discrete value of electromagnetic energy is called the photon. A photon is the minimum quantum packet of energy and represents the smallest indivisible particle of light. Each photon’s energy can be quantified and is proportional to its frequency, as described by Max Planck’s equation E = hu, where E is energy, h is Planck's constant, and u is the frequency. On a submicroscopic scale, energy is often measured in electron volts (eV), which is the energy given to a fundamental charge accelerated through a potential difference of 1 V.