The correct answer is C) States can declare federal laws to be unconstitutional.
The statement that best defines the doctrine of nullification is "States can declare federal laws to be unconstitutional."
In legal terms, the Doctrine of Nullification was created by the Southern states before the initiation of the Civil War. It stated that the Confederate states could declare federal laws to be unconstitutional. The vice president of the United States, John Calhoun, from South Carolina, was the main supporter of the doctrine of nullification. This was also a cause for the US Civil War.