Which relation on A = {1,2,3} is symmetric?

Correct answer: {(1,2),(2,1),(3,3)}

To test symmetry, inspect every non-diagonal ordered pair and check whether its reverse is also present. In option A, (1,2) is accompanied by (2,1), and (3,3) is its own reverse, so the relation is symmetric. Option B lacks (2,1) and (3,2); C lacks (3,1) and (1,2); D lacks (3,2). Therefore only A satisfies the definition.