Let A=\ 0,1,2, , 9\ . Let R be a relation on A defined by (x, y) ∈...

The relation $R$ on $A = \{0,1,2,\ldots,9\}$ is defined by $(x,y) \in R$ iff $|x-y|$ is a multiple of 3, i.e., $x \equiv y \pmod{3}$.
Statement II:
$R$ is reflexive ($|x-x|=0$, a multiple of 3), symmetric ($|x-y|=|y-x|$), and transitive (if $x \equiv y$ and $y \equiv z \pmod{3}$, then $x \equiv z \pmod{3}$). So $R$ is an equivalence relation. Statement II is correct.
Statement I:
The equivalence classes are $\{0,3,6,9\}$ (4 elements), $\{1,4,7\}$ (3 elements), $\{2,5,8\}$ (3 elements).
$n(R) = 4^2 + 3^2 + 3^2 = 16 + 9 + 9 = 34 \neq 36$. Statement I is incorrect.