One responsibility that belongs only to United States citizens is serving on a jury when called.
Citizenship-only responsibilities
Serving on a jury in federal court is limited to U.S. citizens, and non‑citizen residents are generally not eligible to serve. This is why civics and naturalization materials list “serve on a jury” as a correct answer to the question about a responsibility that is only for U.S. citizens.
Another common answer given in official study guides is voting in federal elections, which is also restricted to U.S. citizens by law. Other duties like paying taxes or obeying the law apply to everyone living in the United States, not just citizens.
