Three infectious agents are examined: X contains nucleic acid enclosed by a capsid, Y is free low-molecular-weight RNA w
A virus contains RNA or DNA protected by a protein capsid. A viroid consists of free, low-molecular-weight RNA and lacks a protein coat. A prion is an infectious agent made of abnormally folded protein.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Viruses Viroids Prions and Lichens