Who discovered viroids?

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 $R$?

Which of the following structures can pass through a bacteria-proof filter?

Which virus was discovered first?

Which of the following is not true for viruses?

Lichens are a well-known association between algae and fungi. In this association,the fungus has a/an ..... relationship with the algae.