In thermochemistry, what does a high reactivity to water suggest about an element?

A high reactivity to water indicates that an element readily reacts with H2O to form hydroxides and hydrogen gas. Alkaline earth metals, which are found in Group 2 of the periodic table, are known for their strong reactivity with water, particularly the heavier members like calcium, strontium, and barium. When these metals react with water, they form a metal hydroxide and release hydrogen gas, showing their strong tendency to engage in such reactions.

In contrast, noble gases are characterized by their lack of reactivity under standard conditions, while transition metals display variable reactivity depending on their specific chemistry and oxidation states. Halogens do react with other substances, but their reactions with water are not as pronounced as that of alkaline earth metals. Therefore, the characteristic high reactivity of alkaline earth metals with water makes this option the most suitable answer.