Why does using different age groups increase the validity of a study?

Acriterion for waiving informed consent is that, when appropriate, subjects are provided additional pertinent information after the study. in which of the following studies would it not be appropriate to provide subjects with information about missing elements of consent: a study in which researchers told students that they would be given a quiz after reading some study materials when the researchers did not intend to use a quiz, but were attempting to focus subjects’ attention on the material. a study in which subjects were told that they performed in the third quartile on an anagram task when in reality students were randomly assigned scores that were not related to their actual performance. a study in which subjects were assigned to study activities based on an undesirable or unflattering physical characteristic as assessed by members of the research team. a study involving decision-making games in which subjects were led to believe that they were interacting with another student in another room, but were actually interacting with a computer programmed to provide consistent responses to all subjects.