What substance is characterized by producing OH- ions in aqueous solutions?

The correct answer is based on the fundamental properties of acids and bases in chemistry, particularly regarding their behavior in aqueous solutions. A substance that produces hydroxide ions (OH-) when dissolved in water is classified as a base. This characteristic reaction occurs because bases increase the concentration of hydroxide ions in solution, which is a defining feature of basicity.

When a base dissolves in water, it typically dissociates to release OH- ions. This increase in OH- ions raises the pH of the solution, making it more alkaline. For example, sodium hydroxide (NaOH) dissociates in water to yield Na+ ions and OH- ions. The presence of these hydroxide ions is what gives a solution its basic properties.

Conversely, acids tend to produce hydrogen ions (H+) or protons when dissolved in water, leading to a lower pH and a more acidic solution. By understanding these definitions and reactions, it's clear why the substance that produces OH- ions is identified as a base.

Neither a solvent, which is typically a substance that dissolves another (like water itself), nor a buffer, which helps to maintain pH levels in a solution without significantly changing when an acid or base is added, aligns with the