Final answer:
The patient's belief that he is the president and that terrorists are trying to kidnap him is a delusional symptom, recorded as 'positive behavior' in clinical terms within the field of mental health.
Step-by-step explanation:
A patient who believes himself to be the president of the United States and fears that terrorists are trying to kidnap him is demonstrating a type of psychiatric symptom. When a nurse observes and records these false beliefs, they are documenting behavior that involves delusions. In clinical terms, particularly in the field of mental health, such delusions are typically considered to be positive behavior. This term does not mean 'good' behavior but rather refers to an excess or distortion of normal functions, in this case, delusions and paranoid beliefs. Therefore, the correct answer to the question is b. Positive behavior.