Final answer:
A source qualifier adds credibility or specificity to a piece of historical information, such as 'Second president of the United States' does for John Adams, by providing important aspects of his identity and historical role.
Step-by-step explanation:
Within the context of historical information, a source qualifier is a descriptor or detail that adds credibility or specificity to a piece of information. It helps to affirm the accuracy or authority of a statement by providing additional context. In the question posed by the student, the instance "Second president of the United States" serves as an example of a source qualifier for John Adams because it specifies an important aspect of his identity and historical significance, distinguishing him from others with perhaps the same name or less defined roles. Source qualifiers not only give more information about a subject but also place it within the correct historical framework. For John Adams, additional qualifiers could include details about his role in the early American republic, his diplomatic efforts, and his contributions to foundational documents like the Declaration of Independence. It's the specific and verifying details, such as his presidency, that act as qualifiers in this instance.