Which of the following statements is true regarding viroids in the context of organic chemistry?

• A. Viroids are $\mathrm{DNA}$ molecules that replicate independently in host cells.
• B. Viroids are lipid-based structures that store genetic information.
• C. Viroids are complex proteins that catalyze organic reactions.
• D. Viroids are small infectious agents composed solely of $\mathrm{RNA}$.

Answer: (D)

Verified step by step guidance

1. Understand the nature of viroids: Viroids are small, circular RNA molecules that are capable of infecting plants. They do not encode proteins and rely on the host cell's machinery for replication.
2. Differentiate viroids from other biological entities: Unlike viruses, viroids do not have a protein coat. They are distinct from DNA molecules, lipid-based structures, and proteins.
3. Analyze the given statements: Evaluate each statement based on the known characteristics of viroids.
4. Statement 1: Viroids are DNA molecules that replicate independently in host cells. This is incorrect because viroids are RNA, not DNA.
5. Statement 4: Viroids are small infectious agents composed solely of RNA. This is the correct statement as it accurately describes the nature of viroids.