It should be (n2)3
why (n2)3 ?
did not understand the cube part..
at least 3 equivalence class not exactly 3 is mentioned even if we consider 3 equivalence classes then total number of ordered pairs (according to your previous explanation) becomes 3*n^2 not (n2)3
Oops...I read the question wrong. But still consider
#total elements = k. n2
Now, try to find the factors of any of the answers and check if we can get a perfect square. Since,
k >= 3
we can take k=4 so that we get (D) as the answer.