Question

Virus with nucleic acid but without protein coat is
(a) Virion
(b) Viroid
(c) Capsid
(d) Prion

Answer 1

Virus is made up of nucleoprotein and it is inert outside like macromolecules. The capsid is made up of protein and Virion, Viroids and Prion are part of a virus but show the difference due to the absence or presence of protein and nucleic acids.

Complete answer:
Viroids were discovered by T.O. Diener in 1971 as an infectious agent and it is smaller than a virus and causes disease like potato spindle tuber disease, citrus exocytic disease. It consists of nucleic acid-like RNA but is devoid of protein like nucleoprotein coat. The nucleic acid RNA has low molecular weight and it is present in a circular or linear stranded structure that is tightly folded.

Additional Information:
Virion is an inert virus and it reproduces inside living hosts. It uses enzymes and other metabolic machinery from the host in which it enters and starts spreading infection. It always occurs as obligate intracellular parasites.
Prions are obligate parasites which are made up of protein only and cause disease like scrapie in sheep, mad cow disease, kuru disease etc. Alzheimer disease is also caused by prions.
The capsid is a nucleoprotein which is made up of nucleoid and covered by a portion. It is arranged in the form of subunits called capsomeres.

So, the correct answer is 'Viroid'.

Note:
Sir D.C.Gajdusek was awarded a Nobel prize in 1976 for his discovery of a disease caused by a prion which is also known as a slow virus. Bacteriophage is also a type of virus that infests or destroys the bacteria which cause its death.