Answer:
b.The extent to which a causal relationship found in a study can be generalized beyond the study conditions
Step-by-step explanation:
External validity: In psychology, the term external validity is defined as the magnitude to which a research's conclusion of an individual's research study can be generalized in regards to the people outside that research study. Generalization can be described in terms of environmental, population, and temporal.
The external validity reflects whether the results of a particular research study are meaningful and trustworthy or not. It demonstrates the applicability of research findings to the real world.
Example: Aptitude treatment Interaction.