Final answer:
Strontium (Sr) is more likely to react with bromine (Br) than krypton (Kr), argon (Ar), or oxygen (O) due to its lower second ionization energy and its position in the periodic table as an alkaline earth metal.
Step-by-step explanation:
The element more likely to react with bromine (Br) is strontium (Sr). In comparison to the noble gases krypton (Kr) and argon (Ar) which are inert and unlikely to form compounds due to their complete valence electron shells, Sr, as an alkaline earth metal, has a tendency to lose electrons and form positive ions. Oxygen (O) is reactive as well, but it typically forms anions by gaining electrons, making Sr, with its lower second ionization energy, more likely to form a compound with Br.
Regarding the second ionization energy, Sr has a lower second ionization energy compared to Rb and Ar, as it is easier to remove a second electron from an alkaline earth metal than from a noble gas or an alkali metal cation. Predicting electron affinities based on periodic trends, Rb is more likely to form a gaseous anion, but in this context, we are concerned with reaction potential, placing Sr at the forefront.