Final answer:
Students demonstrate understanding when they correctly identify syphilis as a notifiable disease that must be reported by law. Other STIs like genital herpes and hepatitis B are not notifiable in every jurisdiction.
Step-by-step explanation:
The sexually transmitted infection (STI) that must be reported by law and the one students correctly identify is syphilis. According to the Centers for Disease Control and Prevention (CDC), syphilis is a notifiable disease, meaning that healthcare providers are legally required to report each diagnosis of syphilis to health authorities. This is in contrast to other STIs such as genital herpes (Condylomata acuminata) and hepatitis B, which are not notifiable in all jurisdictions. Notifiable diseases, such as syphilis, are of particular public health importance because of their potential for epidemic spread and severe health consequences, which can include systemic health effects and serious complications if left untreated.