Which type of RNA is the most common in cells?

Ribosomal RNA (rRNA) is indeed the most abundant type of RNA found in cells. This abundance is due to its critical role in the formation of ribosomes, which are essential cellular structures responsible for protein synthesis. Ribosomes are composed of both rRNA and proteins, and in eukaryotic cells, these ribosomes consist of two subunits that include multiple rRNA molecules. Given that each ribosome contains rRNA and that cells have many ribosomes, rRNA naturally accumulates to a higher level than other forms of RNA.

In contrast, messenger RNA (mRNA) serves as a temporary molecule that carries genetic information from DNA to ribosomes for protein synthesis. Transfer RNA (tRNA) is involved in bringing amino acids to the ribosome during translation. Small nuclear RNA (snRNA) is involved in RNA splicing. While all these types of RNA are important for cellular functions, none match the sheer quantity of rRNA because of its structural role in ribosomes present within every cell, thus solidifying its status as the most abundant RNA type.