What is a group in the context of the periodic table?

In the context of the periodic table, a group refers to a column of elements. Elements that are in the same group typically share similar chemical properties and are characterized by having the same number of electrons in their outermost shell, which greatly influences their reactivity and bonding behavior. For instance, the alkali metals in Group 1 all have one electron in their outer shell, making them highly reactive and giving them similar chemical characteristics.

The other options do not accurately describe a group. A row of elements is referred to as a period, not a group. A set of nonmetals could include elements from various groups, and defining a group solely by a category of reactive metals is too narrow; groups encompass a broader range of elements with shared properties rather than being limited to specific reactivity. Understanding that a group is a vertical collection of elements helps clarify how the periodic table organizes elements based on their shared attributes.