Final answer:
Strontium and barium share similar chemical properties due to having the same number of valence electrons, which defines their reactions in chemical processes.
Step-by-step explanation:
Strontium and barium have similar chemical properties because atoms of these elements have the same number of valence electrons. Both strontium and barium are part of the alkaline earth metals group and have two valence electrons. In the periodic table, elements grouped in the same column have the same number of valence electrons, which strongly influences their chemical reactions through the loss, gain, or sharing of these electrons.