Which of the following best describes a strong base?

A strong base is characterized by its ability to dissociate completely in water to release a significant concentration of hydroxide ions (OH-) into the solution. This substantial increase in OH- ions is what leads to a marked increase in the pH level, making the solution highly basic. The high concentration of these ions is responsible for the strong alkaline properties observed in solutions of strong bases.

The first option, suggesting a violent reaction with water, does not accurately define a strong base. While some substances may react vigorously with water, this is not a characteristic of strong bases themselves.

The second option, indicating that a substance does not alter pH levels, contradicts the main feature of a strong base, which is to significantly increase pH through the release of OH- ions.

The final choice, which describes a substance that is only soluble in alcohol, does not align with the definition of a strong base. Strong bases, such as sodium hydroxide or potassium hydroxide, are typically soluble in water.

Thus, the correct option accurately captures the essential characteristic of a strong base: its capacity to produce a large number of hydroxide ions in solution.