Final answer:
Gamma radiation (D) is the form of radiation consisting of electromagnetic radiation or photons, distinguished from alpha and beta particles which are forms of particulate radiation.
Step-by-step explanation:
The form of radiation that is composed of electromagnetic radiation or photons is gamma radiation, which is represented in the question as option D) gamma radiation. Gamma rays are on the electromagnetic spectrum with very short wavelengths and high energy, making them a highly penetrating form of radiation and potentially dangerous to living tissues. Unlike alpha particles, which consist of two protons and two neutrons and are the same as a helium nucleus, or beta particles, which are high-speed electrons, gamma rays do not consist of matter but are a form of energy.