S={(1,2), (2,1)} -> This relation is Irreflexive, Symmetric, Not Transitive, Not Reflexive, Not Asymmetric, Not antisymmetric.
Equivalence Relation -> Symmetric, Transitive, Reflexive.
It is not transitive & Reflexive.
So Reflexive closure of S = { (1,1),(2,2),(3,3),(1,2),(2,1) }
After taking transitive closure relation does not change.
Answer S = { (1,1),(2,2),(3,3),(1,2),(2,1) }
S = {a,b}
P(S) = { $\emptyset$,{a},{b},{a,b}}
Related Hasse Diagram