Which of the following is a physical identifier to check on an ID?

A physical identifier on an ID is a characteristic that can be observed directly and is typically present for identification verification purposes. Eye color fits this definition perfectly, as it is a distinct physical trait that can be easily matched with the individual’s appearance at the time of ID verification. Checkers often look for such identifiers to ensure that the person presenting the ID is indeed the individual to whom the ID belongs.

The other options, while they may provide additional personal information, do not serve as direct physical identifiers. Graduation year, for instance, pertains to a specific event in a person's life, and favorite color is a subjective preference that does not provide verifiable physical characteristics. Address can indicate where an individual lives but does not relate to their physical appearance. Thus, among the choices presented, eye color stands out as the correct answer, as it is a verifiable physical attribute directly observable during ID checks.