The modification of behavior by study participants in response to their knowledge that they are being observed or singled out for special treatment is known as:

Correct option is B

The Hawthorne effect refers to the phenomenon where individuals modify their behavior because they are aware that they are being observed, or because they feel they are receiving special treatment. This effect was originally identified in studies at the Western Electric Hawthorne Works in the 1920s and 1930s.
Explanation of options: (a) ✘ Incorrect. The term "reactive effect" is not specifically used to describe this phenomenon, although it is related to changes in behavior due to observation. (b) ✔ Correct. The Hawthorne effect specifically refers to behavior modification due to awareness of being observed. (c) ✘ Incorrect. The "novelty effect" refers to changes in behavior due to the novelty of an intervention, not the awareness of being observed. (d) ✘ Incorrect. The "experimental effect" is a general term that could refer to changes in behavior caused by any experimental condition but is not specifically linked to the awareness of observation.