Which quality is associated with a mercurial individual?

A mercurial individual is characterized by their tendency to be changeable and unpredictable, especially in their moods or emotions. This term derives from the element mercury, which is known for its liquid form and ability to shift rapidly from one state to another. Consequently, the correct answer highlights the qualities of being quick-tempered and changeable, which aligns with the essence of mercurial behavior.

In contrast, the other options reflect stable qualities. Being constant and predictable describes individuals who maintain consistent behavior and responses over time, which inherently opposes the notion of being mercurial. Similarly, calm and composed individuals exhibit emotional steadiness, showing little variability in their demeanor. Lastly, diligent and industrious describe a hardworking and focused nature, again lacking the transformative and fleeting traits characteristic of a mercurial disposition.