Step 1: Understanding the Concept
A biodegradable polymer is broken down by microorganisms in nature.
Step 2: Check the Polymers
Nylon 6 and Nylon 6,6 are synthetic polyamides which are not biodegradable.
Step 3: Conclusion
Viscose rayon is regenerated cellulose, a natural based polymer that is biodegradable. Option (D).
Final Answer:
Viscose rayon is biodegradable.
\[ \boxed{\text{(D) }\text{Viscose rayon}} \]