How does reactivity change as you go down a metal group?

For Groups 1, 2 & 3 it becomes more reactive.
However the Transition Metals are different. In the case of Copper , Siler & Gold, they becomes less reactive as you go down the group.

Reactivity of metals depends on their ability to lose electron. The more easily they lose electrons (lower ionization energy), the more reactive they are. As u go down the group, the ability to lose electron increases (i.e the ionization energy decreases) thus the reactivity increases.