For an ideal gas, internal energy (U) depends only on:
Temperature is the scientifically accurate answer to this question. Within the study of Kinetics and Thermodynamic, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of Temperature directly address what is being asked. Among the other options, Pressure, Volume, and Gibbs free energy do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Campbell Biology, Urry et al., 12th Ed.