Question

strontium and barium have similar chemical properties because atoms of these elements have the same number of
protons
valence electrons
neutrons
electron shells

Explanation:

Strontium (Sr) and barium (Ba) are in the same group (Group 2, alkaline earth metals) of the periodic table. Elements in the same group have the same number of valence electrons. Chemical properties are mainly determined by the number of valence electrons. Protons determine the element's identity, neutrons affect isotopes, and electron shells (energy levels) increase down a group, but valence electrons (outermost electrons) are the same for group members, leading to similar chemical properties.

Answer:

B. valence electrons