Refers to the ability of an instrument or tool to accurately measure what it is supposed to measure. 1. operational definition 2. generalizability 3. validity 4. reliability

Validity refers to the ability of an instrument or tool to accurately measure what it is supposed to measure.

Explanation:

The option 1 is not correct as the operational definition tell us about the operations and terms involved in a process. The option 2 is incorrect as generalizability refers to the general properties or behavior of a thing.The option 3 is correct as validity defines the correctness of a concept or accuracy of something like an instrument. This word is derived from Latin word Validus that means strong. So, it is the ability of an instrument to measure something accurately.The option d is not correct as the reliability defines whether we can trust something or not. It tells consistency of a an experiment or tool  whether it is being performing or accurately or not.