Final answer:
Gamma rays, which are uncharged, will travel through an electric field without being deflected and have the greatest penetration power among alpha, beta, and gamma radiation.
Step-by-step explanation:
The kind of radiation that will travel through an electric field on a pathway that remains unaffected by the field is gamma ray (Option C). Gamma rays are a high-energy form of electromagnetic radiation, which, unlike charged particles such as protons, electrons, and alpha particles, have no electric charge and thus will not be influenced by electric or magnetic fields. Gamma rays have tremendous penetration power and are able to pass through dense materials such as lead, whereas other types of radiation like alpha and beta particles are deflected due to their charge. Ionizing power is least significant for gamma rays because they do not readily produce ionization effects on the materials they pass through, due to the lack of charge.