The increasing order of the reactivity of Zn, Cu, Fe, and Ag is

Metal reactivity series:

The reactivity series is a list of metals arranged in order of their reactivity, from most reactive to least reactive.

Potassium > Sodium > Calcium > Magnesium > Aluminum > Zinc > Iron >  Lead > Hydrogen > Copper > Mercury > Silver > Gold > Platinum

The increasing order of the reactivity of Zn, Cu, Fe, and Ag is Ag < Cu < Fe < Zn.
A less reactive metal can be displaced by a more reactive metal from its salt solution. Zinc replaces copper and iron in their salt solutions. So, zinc is more reactive than copper and iron. Copper replaces silver in silver nitrate. So, copper is more reactive than silver. In copper and iron, copper is less reactive because it cannot replace iron in ferrous sulphate solution.