Who discovered the virus for the first time?

Which of the following structures contains a short strand of $RNA$?

$A$: Viroids lack a protective protein coat called a capsid.
$R$: Viroids contain a short strand of $DNA$.

Assertion $A$: Viruses are considered as a link between living and non-living organisms.
Reason $R$: Viruses are non-living,but they are obligate parasites in living cells.
Which option is correct for Assertion $A$ and Reason $R$?

Phages that show a lysogenic cycle are called:

What does the part labeled $''A''$ in the given figure represent?