Q.The most stable RNA is:

rRNA (ribosomal RNA) is the most stable of the RNA types because of its highly folded, extensively base-paired structure and its permanent structural role within ribosomes.

Cells contain three major types of RNA — mRNA, tRNA, and rRNA — which differ greatly in abundance, structure, and turnover rate:

• mRNA (messenger RNA) is the least stable; it is synthesised, used briefly as a template for translation, and then rapidly degraded, allowing the cell to regulate protein synthesis dynamically.
• tRNA (transfer RNA) is a small, relatively stable RNA with a cloverleaf secondary structure, but it is much less abundant than rRNA. …

tRNA is called "soluble RNA" because, being the smallest RNA molecule (about 75-90 nucleotides, cloverleaf-shaped), it stays freely soluble in the cytoplasm rather than remaining associated with ribosomes the way rRNA does.

Of the three major classes of RNA:

• mRNA (messenger RNA) carries the genetic code from DNA to the ribosome for protein synthesis; it is comparatively large and linear.
• rRNA (ribosomal RNA) is a structural and catalytic component of ribosomes, tightly bound within the ribosome's large and small subunits. …