A relation R in a set A is transitive if $\left({\mathit{a}}_1,{\mathit{a}}_2\right)$ ∊ R and $\left({\mathit{a}}_2,{\mathit{a}}_3\right)$ ∊ implies $\left({\mathit{a}}_1,{\mathit{a}}_3\right)$ ∊ R, where ${\mathit{a}}_1,{\mathit{a}}_2,{\mathit{a}}_3$ ∊ A
Now, (1, 2), (2, 1) ∊ R, but (1, 1) ∉ R
Thus, the given relation R is not transitive.