RNA polymerase I catalyst synthesis of ribosmal RNA(r RNA). this RNA account more over 50% in cells. this is mostly occurred in prokaryotic cells. so answer is option A

RNA Polymerase I and rRNA Synthesis
RNA polymerase I is responsible for catalyzing the synthesis of ribosomal RNA (rRNA) in eukaryotic cells. This enzyme plays a crucial role in the production of ribosomes, which are essential for protein synthesis.

Process of rRNA Synthesis
- RNA polymerase I binds to specific regions of DNA called rRNA genes.
- The enzyme then unwinds the DNA double helix and begins transcribing the gene into a complementary RNA molecule.
- The newly synthesized rRNA is processed and modified before being assembled into ribosomes.

Importance of rRNA
- Ribosomal RNA is a key component of ribosomes, which are the cellular machinery responsible for protein synthesis.
- The accurate and efficient synthesis of rRNA is essential for the proper functioning of the cell.

Role of RNA Polymerase I
- RNA polymerase I is specialized for transcribing rRNA genes and is highly efficient in this process.
- The enzyme ensures that an adequate supply of rRNA is produced to support the protein synthesis needs of the cell.

Conclusion
In summary, RNA polymerase I plays a crucial role in catalyzing the synthesis of ribosomal RNA, which is essential for protein synthesis in eukaryotic cells. This enzyme is specialized for transcribing rRNA genes and is vital for maintaining the proper functioning of the cell.