Step 1: Concept
A relation is symmetric if $(a, b) \in R$ implies $(b, a) \in R$.
Step 2: Analysis
In the given relation $R$, we have $(2, 3) \in R$. For the relation to be symmetric, $(3, 2)$ must also be in $R$.
Step 3: Conclusion
Since $(3, 2) \notin R$, the relation is not symmetric.
Final Answer: (D)