Which ion is indicative of a strong base?

The presence of the hydroxide ion (OH-) is indicative of a strong base. A strong base is defined as a substance that completely dissociates in solution to produce hydroxide ions. When a strong base dissolves in water, it generates a high concentration of OH- ions, which leads to an increase in pH and basicity of the solution.

In the context of acid-base chemistry, bases are substances that can accept protons (H+) or donate electron pairs. The hydroxide ion specifically reacts with protons in solution, neutralizing acids and contributing to the basicity of the environment. The higher the concentration of hydroxide ions, the stronger the base.

Therefore, the presence of hydroxide ions is a clear indicator of a strong base, making it the correct choice in this scenario.