Which observation does the CLASSICAL wave theory of light FAIL to explain for the photoelectric effect?

1. The classical wave theory says light's energy is continuous and depends only on amplitude (intensity). So a bright-enough source of ANY frequency should eventually deliver enough energy to free an electron. 2. Experiment shows the opposite: BELOW a threshold frequency $\nu_0$, the photocurrent is exactly zero regardless of intensity or exposure time. This is the failure that classical theory cannot reconcile. 3. Einstein resolved it by quantising light into photons of energy $h\nu$: if $h\nu < \phi_0$, no single photon has enough energy to free an electron, so no current. 4. Option A is consistent with both theories (more energy → more emissions). Options C and D are about the SHAPE of the current-voltage curve, which classical theory handles fine. Only B is the genuine classical failure. _Source: NCERT Class 12 Physics Part 2, Ch 11, §11.5 (Photoelectric effect and wave theory of light) — explicitly listed failure, p. 6 ¶2._