What is the basic composition of a virus?

Viruses are fundamentally composed of a nucleic acid core, which can be either DNA or RNA, surrounded by a protein coat known as a capsid. This structure is essential for the virus's ability to infect host cells, as the nucleic acid contains the genetic information necessary for replication and the capsid helps protect this genetic material, as well as assist in the entry of the virus into host cells.

In contrast, the other options do not reflect the true nature of a virus. The notion of a virus being a single cell with a cell wall mischaracterizes viruses, as they are not cellular organisms and lack cellular structures like walls. A complete ribosomal structure refers to components involved in protein synthesis found in living cells, but viruses do not possess ribosomes or other cellular machinery to carry out metabolic processes. The description of a strand of DNA surrounded by cytoplasm misconstrues viruses, since they do not have cytoplasm or cellular components; they exist only as nucleic acid and protein. This makes the first option the accurate representation of viral composition.