Final answer:
Between Calcium and Gallium, Gallium is the least reactive. Calcium, as an alkaline earth metal, readily sheds electrons, becoming more reactive. However, Gallium does not shed electrons as easily, which allows it to form stronger bonds and exhibit less reactivity.
Step-by-step explanation:
The element least reactive between calcium (Ca) and gallium (Ga) would be gallium (Ga). This is mainly because of their positions in the periodic table. Gallium is found in Group 13 of the periodic table, where it's electron configuration leads to more stable and less reactive characteristics compared to elements in Group 1 and 2, like calcium.
Calcium (Ca) resides in Group 2 of the periodic table and is an alkaline earth metal. Metals in this group are known to lose their outer electrons easily in an effort to achieve a noble gas configuration. This results in Ca readily forming a Ca²+ ion, thus making it more reactive.
On the other hand, gallium (Ga) does not readily lose electrons to form ions, making it less reactive. In all of the given options, Option 2 is the closest to this explanation. So, gallium (Ga) is less reactive because it forms stronger bonds, not because it's a noble gas as suggested in Option 4. Noble gases are in Group 18 of the periodic table, and gallium does not belong to that group.
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