What is a base in terms of its effect on hydrogen ion concentration?

A base is defined as a substance that decreases the hydrogen ion (H⁺) concentration in a solution. This characteristic is often associated with the properties of bases in chemistry, where they tend to accept protons or release hydroxide ions (OH⁻) in an aqueous solution. When a base is dissolved in water, it can react with hydrogen ions present in that solution, effectively reducing their concentration.

In contrast, an acid increases the hydrogen ion concentration, which is the opposite of what bases do. The third option captures this fundamental characteristic of bases accurately.

Additionally, while some substances may not significantly alter hydrogen ion concentrations, this does not align with the core definition of a base. Similarly, the notion that a base can only neutralize acids is overly restrictive, as bases can exist and act in solutions without necessarily being in the presence of acids. Thus, the definition focused on the reduction of hydrogen ion concentration illustrates the primary behavior of bases effectively.