Solution:

For an ideal gas, internal energy depends only on temperature. For a real gas, intermolecular forces exist, giving rise to internal potential energy in addition to kinetic energy. The internal kinetic energy depends on temperature, while the internal potential energy depends on the average distance between molecules, which is related to the volume. Thus, Assertion (A) is true, and Reason (R) is true. Reason (R) provides the accurate explanation for why the internal energy of a real gas is a function of both temperature and volume.