A complete virus particle, known as a virion, consists of nucleic acid surrounded by a protective coat of protein called a capsid. These are formed from identical protein subunits called capsomeres. Complex viruses code for proteins that assist in the construction of their capsid.

The correct answer is option B) Virion.

Explanation:
A virus is a microscopic infectious agent that can only replicate inside the cells of a living host. The infective unit of a virus is called a virion.

A virion is a complete virus particle that consists of a nucleic acid genome (either DNA or RNA) surrounded by a protein coat called a capsid. The nucleic acid contains the genetic information of the virus, which is necessary for its replication and functioning.

Here is a detailed explanation of the components of a virion:

1. Nucleic Acid Genome:
- The nucleic acid genome of a virus can be either DNA or RNA.
- It carries the genetic information necessary for viral replication and the synthesis of viral proteins.
- The genome may be single-stranded or double-stranded, depending on the virus.

2. Capsid:
- The capsid is a protein coat that surrounds and protects the viral genome.
- It is composed of repeating protein subunits called capsomeres.
- The capsid provides structural integrity to the virion and helps in the attachment of the virus to host cells.
- It can have various shapes, such as helical, icosahedral, or complex, depending on the type of virus.

3. Envelope (optional):
- Some viruses have an additional outer layer called an envelope.
- The envelope is derived from the host cell's membrane and contains viral proteins.
- It helps the virus in evading the host's immune system and facilitates entry into host cells.
- Not all viruses have an envelope, and those without an envelope are called non-enveloped or naked viruses.

4. Other Proteins:
- Besides the capsid, virions may contain other proteins that are necessary for viral replication or host interaction.
- These proteins may include enzymes for viral genome replication, proteins involved in viral assembly, or proteins that aid in host cell entry.

In summary, a virion is the infective unit of a virus that consists of a nucleic acid genome (DNA or RNA) surrounded by a protein coat (capsid). It serves as a complete infectious particle capable of entering and infecting host cells.