Assertion: True. Experiments show that photoelectrons are emitted almost instantaneously after illumination, with no measurable time delay.
Reason: True. According to classical wave theory, energy is spread continuously across the wavefront. At very low intensities, an electron would need a long time to accumulate sufficient energy to escape, which contradicts experimental observations. This was a major limitation of the wave model.
Relationship: Although both statements are true, the reason does not correctly explain the assertion. The spontaneity of emission is actually explained by the photon model, where energy is transferred in discrete packets, not by the classical wave description mentioned in (R).