The correct choice is (c) 49
Easiest explanation: Let R is an equivalence relation on the set S and so it satisfies the reflexive, symmetric and transitive property. The largest equivalence relation means it should contain the largest number of ordered pairs. Since we can have n^2 ordered pairs in R x R where n belongs to S and all these ordered pairs are present in this relation; its the largest equivalence relation.So there are n^2 elements i.e 7^2 = 49 elements in the largest equivalence relation.