What type of RNA carries instructions for protein synthesis from the nucleus to the ribosome?

Messenger RNA (mRNA) is responsible for carrying genetic instructions from the nucleus to the ribosome, where proteins are synthesized. It is synthesized during the transcription process, wherein the DNA sequence of a gene is copied to produce a complementary RNA strand. After mRNA is formed, it exits the nucleus through nuclear pores and travels to the ribosome in the cytoplasm, where it serves as a template for protein synthesis during translation.

Ribosomal RNA (rRNA) is a component of ribosomes, providing structural support and playing a role in the catalytic activity of the ribosome but does not carry genetic instructions. Transfer RNA (tRNA) is involved in the actual process of translation by bringing the appropriate amino acids to the ribosome, matching them to the codons on the mRNA, but it does not carry instructions from the nucleus. Small nuclear RNA (snRNA) is primarily involved in the processing of pre-mRNA in the nucleus, such as splicing introns from the RNA transcript, rather than in transporting instructions for protein synthesis.

Thus, mRNA is the correct answer as it uniquely fulfills the function of transmitting the genetic blueprint from DNA in the nucleus to the sites of protein synthesis, the ribosomes.