Which of the following best describes a base?

A base is best described as a substance that produces hydroxide ions in solution. When a base dissolves in water, it dissociates to release hydroxide ions, which contribute to the increase in pH above 7. This characteristic defines bases distinctly from acids, which release hydrogen ions and have a pH less than 7.

This definition is foundational in acid-base chemistry and highlights the role of hydroxide ions in neutralization reactions, where they can combine with hydrogen ions to form water. Therefore, the production of hydroxide ions is a key feature that signifies a substance's basicity.

In contrast, substances described as having a pH less than 7 that donate protons would correctly characterize an acid, illustrating why this choice does not accurately describe a base. Similarly, while bases do react with acids to form salts, not all bases are necessarily involved in this reaction, making that choice too limiting. Lastly, the characteristic of having a sour taste pertains to acids rather than bases. Thus, the option that encompasses the essence of a base is the one focused on the production of hydroxide ions.