The statement that is always true about the literary genre of satire is:
b. It employs an ironic or sarcastic tone.
Satire is characterized by the use of irony, sarcasm, and exaggeration to criticize or mock subject matter, often relating to social, political, or cultural issues. While satire can certainly amuse the reader (option c), that is not its defining characteristic, and it doesn't necessarily include political elements (option a) or aim to confuse or unsettle readers (option d).