Which statement gives the correct definition of a symmetric relation?

Correct answer: If (a,b) ∈ R, then (b,a) ∈ R

Symmetry is defined by reversal of ordered pairs. A relation R is symmetric when, for every a and b in its underlying set, the presence of (a,b) in R guarantees the presence of (b,a) in R. Option A states this condition directly and is therefore correct. Option B requires every self-pair and defines reflexivity, not symmetry. Option C requires completion of a two-step chain and defines transitivity. Option D describes the empty relation, which is indeed symmetric but is not the definition of all symmetric relations; many non-empty relations are symmetric as well. Thus only option A gives the general definition rather than a special example or a different property.