Which of the following is a non-cellular parasite consisting of nucleic acid surrounded by a protein coat?

A non-cellular parasite composed of nucleic acid encased in a protein coat is indeed classified as a virus. Viruses lack cellular structures and metabolic processes that are typical of living organisms; instead, they consist solely of genetic material (either DNA or RNA) surrounded by a protective protein coat known as a capsid. This simple structure allows viruses to invade host cells and hijack the cellular machinery to replicate themselves, which is why they are considered obligate parasites.

In contrast, prions are infectious agents composed of misfolded proteins and do not contain nucleic acid, thus not fitting the description provided. Bacteria and protozoa are both cellular organisms with complex structures and functions; bacteria are prokaryotes, while protozoa are eukaryotic microorganisms. Neither of these categories aligns with the definition of a non-cellular parasite as outlined in the question.