Which class of nonmetals is known for its high reactivity?

The halogens are a class of nonmetals known for their high reactivity, primarily due to their electronic configuration. Halogens, found in Group 17 of the periodic table, have seven valence electrons and are only one electron short of a complete octet, which makes them highly eager to gain that additional electron to achieve stability. This propensity to gain an electron leads to their strong reactivity, particularly with alkali metals and alkaline earth metals, which readily donate electrons.

Halogens exhibit a variety of chemical behaviors, such as forming salts with metals and engaging in reactions with other nonmetals. Their high reactivity decreases as you move down the group from fluorine to iodine because the atomic size increases, leading to a greater distance between the nucleus and the valence electrons, thereby reducing the effective nuclear charge experienced by the outermost electron.

In contrast, noble gases are known for their lack of reactivity due to having a complete valence shell. Alkali metals and alkaline earth metals, while also reactive, belong to different categories and are metals rather than nonmetals, which sets them apart from halogens in the context of the question.