During gene expression, dna is transcribed into rna in the nucleus. then, the rna is translated into proteins in the cytoplasm. through what physical barrier must the rna pass when moving from the nucleus into the cytoplasm?

The physical barrier that the mRNA must pass is the nuclear membrane.

The process of gene expression involves two main stages; transcription; the production of messenger RNA by the enzyme RNA polymerase, and the processing of the mRNA molecule. Then the process of translation which takes place outside the nucleus, therefore the mRNA must cross the nuclear membrane to enter the cytoplasm.