Metals differ in their tendency to release valence electrons. The chemical name for this tendency to release electrons is activity. The activity series is the arrangement of elements according to their ability to release electrons.
The activity series is shown below. Li>K>Ba>Sr>Ca>Na>Mg>Al> Mn>Zn>Fe>Cd>Co>Ni>Sn>Pb>H2>Cu Ag>Hg>Au