The given relation R in the set {1,2,3} is defined as R={( 1,2 ),( 2,1 )}.
( 1,1 )∉R. Hence, R is not reflexive.
( 1,2 )∈R and ( 2,1 )∈R. Hence, Ris symmetric.
( 1,2 ) and ( 2,1 )∈R, but ( 1,1 )∉R. Hence Ris not transitive.
Therefore, the given relation R={( 1,2 ),( 2,1 )} in set {1,2,3} is symmetric but neither reflexive, nor transitive.