Which term encapsulates the ability to produce fertile offspring in a species?

The term that encapsulates the ability to produce fertile offspring in a species is "species." A species is typically defined as a group of organisms that can interbreed and produce viable, fertile offspring under natural conditions. This biological concept emphasizes the reproductive isolation between different species, meaning that members of a species are more closely related to one another and can successfully mate, while members of different species generally cannot produce fertile offspring.

Other terms provided do not convey this concept. Solvation refers to the interaction of solvent molecules with solute particles, which is a concept relevant to chemistry rather than biology. Speciation describes the process by which new species arise, which involves reproductive barriers and evolutionary changes, but does not directly refer to the capability of existing species to produce fertile offspring. Specific heat capacity pertains to the amount of heat energy required to change the temperature of a substance, a thermodynamic principle, and also does not relate to the biological definition of species.