Answer:
[2] It was common for an enslaved person to stop there on their way to the North.
Explanation:
Pronoun-antecedent agreement refers to the correspondence in number between the pronoun (which stands for a noun) and the antecedent (which is the word the pronoun stands for). As a result, a singular pronoun must agree with a singular antecedent, and a plural pronoun must agree with a plural antecedent.
In the example sentence, the pronoun their does not agree in number with the antecedent an enslaved person. The revised versions are the following:
It was common for an enslaved person to stop there on his or her way to the North.
Or:
It was common for enslaved people to stop there on their way to the North.
