Which of the following is not an essential part of a virus?

Explanation

Viruses are acellular infectious agents that consist mainly of nucleic acid and a protein coat, and sometimes an outer envelope. The nucleic acid (either DNA or RNA) is the most essential part, as it carries the genetic instructions needed for replication inside a host cell. The capsid, a protective protein coat surrounding the nucleic acid, is also essential because it safeguards the viral genome from damage and helps in attaching to and penetrating host cells. In contrast, the envelope-a lipid layer derived from the host cell membrane-is not essential, since many viruses can survive and remain infectious without it. While the envelope provides advantages like immune evasion and easier entry into host cells, only the nucleic acid and capsid are universally required for a virus to exist and function.