Which term refers to the ability to reason speedily and abstractly, generally decreasing during late adulthood?

The correct choice, which refers to the ability to reason speedily and abstractly, is fluid intelligence. This type of intelligence encompasses the capacity for logical reasoning and problem-solving in new situations, independent of previously acquired knowledge. As individuals age, many studies suggest that fluid intelligence can decline, leading to a decrease in the ability to think abstractly and solve novel problems quickly.

Crystallized intelligence, in contrast, relates to the knowledge and skills that individuals accumulate over time, often improving or remaining stable into late adulthood. Practical intelligence involves the ability to adapt to changing environments and solve everyday problems, while emotional intelligence refers to the ability to recognize and manage one's own emotions and the emotions of others. These latter forms of intelligence are not primarily characterized by speed and abstract reasoning, which is why they do not fit the description provided in the question.