In which instance does federal law take precedence?

Federal law takes precedence when there is a conflict between state law and federal law. This principle is rooted in the Supremacy Clause of the U.S. Constitution, which asserts that the Constitution, as well as federal laws and treaties made under its authority, shall be the supreme law of the land.

When a state law contradicts a federal law, the federal law will prevail, meaning that the state law cannot be enforced in that instance. This ensures consistency in legal standards across the country and upholds the authority of federal legislation over state legislation.

In contrast, the other choices do not accurately represent when federal law takes precedence. Popularity of laws doesn't determine their legality; local government approval is not necessary for a federal law to supersede state law; and while international treaties can impact federal law, the priority of federal law over conflicting state laws is the more precise scenario described in the correct answer.