Electron emission occurs from a photosensitive metal upon photon incidence if the photon energy \( hu \) exceeds the metal's work function \( hu_0 \). The photon's energy is partitioned into overcoming the work function and providing kinetic energy to the emitted electron.
The energy balance is expressed as:
\[ hu = hu_0 + KE_{\text{max}} \]
where \( KE_{\text{max}} \) denotes the maximum kinetic energy of the liberated electrons.
Rearranging yields:
\[ KE_{\text{max}} = hu - hu_0 \]
This equation indicates that the highest kinetic energy of emitted electrons equals the incident photon energy minus the material's work function.
Consequently, the accurate statement among the given choices is: Maximum K.E.=hu−hu_0.