Identify the correct adjective in this sentence: He is a legal resident of the United States.

In the sentence, "He is a legal resident of the United States," the word "legal" serves as an adjective that specifies the type of resident being described. In this context, "legal" indicates that the person's residency is recognized by law, meaning they have the legal right to reside in the United States. This choice directly relates to the lawful status of the individual's residence, which is crucial in distinguishing between those who may reside in a country without official permission and those who have the legal authority to do so.

The other options do not accurately convey the same meaning. "Allowed" implies permission but does not specifically address legal status. "Registered" suggests that there might be an official record of the person, which is relevant but not as definitive as the term "legal." "Certified" typically refers to a confirmation or validation by an authority, which again does not directly relate to residency status in the way that "legal" does. Hence, "legal" is the most appropriate adjective to describe the individual's residency in this context.