Ans. is 'b' i.e., Capsid Structure of virus . The extracellular infectious virus paicle is called as the virion. . The virion consist of a nucleic acid surrounded by a protein coat, the capsid. . The capsid with the enclosed nucleic acid is known as the nucleocapsid. . Two kinds of symmetry are encountered in the capsid a) Icosahedral (cubical) b)Helical . Virion may be enveloped or nonenveloped (naked) . Envelope is lipoprotein in nature, lipid is derived from host cell, while protein is virus coded. . Enveloped viruses are susceptible to the action of lipid solvents like ether, chloroform and bile salts.