What type of chemical releases hydroxyl ions (OH-) in solution?

The correct choice is based on the understanding of how different types of chemicals interact with water and how they affect pH. Bases are defined as substances that can accept protons or donate hydroxyl ions (OH-) in a solution. When a base is dissolved in water, it dissociates and increases the concentration of hydroxyl ions in the solution, which results in a higher pH and a more alkaline environment.

In contrast, amino acids primarily act as buffers and can exist as both acids and bases depending on the pH of the environment, but they do not inherently release hydroxyl ions in a solution. Acids, on the other hand, produce hydrogen ions (H+) when dissolved, which lowers pH and does not contribute to hydroxyl ion concentration. Salts are compounds resulting from the reaction of acids and bases and in their dissociation, they may not necessarily release hydroxyl ions or can vary based on the ions involved.

Thus, understanding the fundamental behavior of bases in water is key to recognizing why they are responsible for releasing hydroxyl ions (OH-) in a solution, making them the correct answer.