Which is the least active metal according to the activity series of metals?
Platinum/Gold/Silver
The activity or reactivity of a metal depends on its ionisation potential. A metal with the least is supposed to be the most reactive as it loses the valence electrons by consuming minimum energy. Ionisation energy, decreases when you move top to bottom in periodic table.
Here, Platinum, Gold and Silver are metals which have higher Ionisation potential ,so they are least reactive metals according to the activity series of metals.