Final answer:
In the Eddington standard model, radiation pressure is represented by the symbol P_radiation, which is a fundamental concept in the study of star dynamics and structure.
Step-by-step explanation:
In the context of the Eddington standard model, the symbol that represents radiation pressure is a). P_radiation. This model assumes that the total pressure within a star is a fixed fraction of the radiation pressure. Radiation pressure, denoted by Prad in physics, is the pressure exerted by electromagnetic radiation on any surface it encounters and can be of considerable importance in astrophysics and cosmology, especially when analyzing the structural integrity and evolution of stars.