**Answer:**

The correct answer is option 'B' - RNA polymerase.

**Explanation:**

Transcription is the process by which RNA is synthesized from a DNA template. It involves the conversion of DNA nucleotide sequence into an RNA nucleotide sequence. The enzyme responsible for transcription is RNA polymerase.

**RNA Polymerase:**
- RNA polymerase is an enzyme that catalyzes the synthesis of RNA from a DNA template during transcription.
- It binds to a specific DNA sequence called the promoter region, which is located upstream of the gene to be transcribed.
- RNA polymerase recognizes the promoter sequence and initiates the unwinding of the DNA double helix.
- It then starts synthesizing a complementary RNA molecule using the DNA strand as a template.
- The RNA polymerase adds nucleotides to the growing RNA chain in a 5' to 3' direction, following the base-pairing rules (A with U, G with C).
- The process continues until the RNA polymerase reaches a termination sequence, which signals the end of transcription.

**Types of RNA Polymerase:**
There are three main types of RNA polymerase in eukaryotic cells:
1. RNA polymerase I (Pol I): Responsible for transcribing ribosomal RNA (rRNA) genes, which are involved in protein synthesis.
2. RNA polymerase II (Pol II): Responsible for transcribing protein-coding genes into messenger RNA (mRNA), which carries the genetic information from the DNA to the ribosomes for translation.
3. RNA polymerase III (Pol III): Responsible for transcribing transfer RNA (tRNA) genes and other small non-coding RNAs.

**Conclusion:**
RNA polymerase is the enzyme responsible for transcription. It catalyzes the synthesis of RNA from a DNA template by adding nucleotides to the growing RNA chain. There are three types of RNA polymerase in eukaryotic cells, with RNA polymerase II being responsible for transcribing protein-coding genes.