One of the most unusual aspects of virus particles is the absence of all organelles and other smaller structures. whereas cells

The tough shell made of protein of the viruses is called capsid (Solution A). The protomers are the subunits if this shell, which are made of protein. The structure of the capsid is either helical or icosahedral.
When a virus infects a cell it begins to replicate itself  and during this process new subunits (new protomers) are synthesized according to the genetic material of the virus.

Caspid

Explanation:

It is the protein shell which contains the nucleic acid. The shell is comprised of the proteins that are organized in subunits called Capsomers.

Functions of caspid:

1) It gives the nucleic acid protection from enzymes which can digest it

2) There are special sites on its surface that help it to attach to a host cell

3) Contains proteins that help the virion to enter the host cell membrane

4) Sometimes under favourable conditions,viral RNA with some other proteins can assemble the caspid to become infectious virus.

The protein covering of a virus is called a capsid.

The capsid is the tough outer protective shell of a virus particle.