Final answer:
Fluorine and lithium are the pair of elements most likely to react when bought together. This reaction is an example of compound formation.
Step-by-step explanation:
The pair of elements that is most likely to react when bought together is fluorine and lithium.
Fluorine is a highly reactive element that readily gains one electron, while lithium readily gives up one electron. When they react, lithium transfers its extra electron to fluorine.
This reaction is an example of a compound formation reaction, where elements combine to form a new compound.