The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by which of the following physical processes ?

The minimum energy required for the electron emission from the metal surface can be supplied to the free electrons by one of some physical processes. What are they.

The minimum energy required to remove an electron is called

The minimum energy required to remove an electron is called

The minimum energy required to eject an electron from an atom is called

The minimum energy required to eject an electron from an atom is called

The energy required to emit an electron from the surface of a metal is called