The type of RNA that carries instructions from DNA in the cell nucleus to the ribosome in the cytoplasm is messenger RNA (mRNA).

Here's how it works:

1. Transcription: DNA in the nucleus serves as a template for the creation of mRNA. This process is called transcription.

2. mRNA Processing: The newly formed mRNA molecule undergoes modifications to become functional, such as the addition of a cap and tail.

3. Export: The processed mRNA molecule is transported out of the nucleus and into the cytoplasm.

4. Translation: At the ribosome, the mRNA molecule is "read" and translated into a chain of amino acids, ultimately forming a protein.

So, mRNA acts as a messenger, carrying the genetic code from DNA to the ribosome where proteins are synthesized.