Which metal in Period 5 is very reactive and has two valence electrons in each atom?

Strontium (Sr) is in Period 5 and Group 2, the alkaline earth metals. Group 2 atoms have two valence electrons and are reactive metals, so strontium matches both clues. Rubidium has one valence electron, while zirconium and silver do not have two outer-shell valence electrons in the usual group-based description.

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