Define the work function of a metal and write its unit.

(N/A) The work function of a metal is defined as the minimum amount of energy required by an electron to just escape from the metal surface.
It is a characteristic property of the metal and depends on the nature of the metal and its surface conditions.
The $SI$ unit of work function is the Joule $(J)$,but in atomic and nuclear physics,it is commonly expressed in electron-volt $(eV)$,where $1 \ eV = 1.602 \times 10^{-19} \ J$.