Probably college/university. A "freshman" is a first year student in high school or college. But freshmen in high school rarely take chemistry.

That will refer to university, as a freshman is a first year student at university or college.

In general, it's ambiguous, since "freshman" refers both to ninth graders (first year of U.S. high school) and first-year college students. But as Angela points out, it's unlikely that a ninth grader would be taking chemistry.