Arrange the following metals in the decreasing order of reactivity: K, Na, Zn, Cu, Hg, Ag

This order reflects the decreasing reactivity of the metals, with Potassium (K) and Sodium (Na) being highly reactive alkali metals, followed by Zinc (Zn), a moderately reactive transition metal. Copper (Cu), Mercury (Hg), and Silver (Ag) are less reactive metals. The reactivity series helps in predicting the outcomes of reactions, such as displacement reactions and metal extractions.