Which plant virus was observed 1st under electron microscope?

Answer: Option C

TMV plant virus was observed 1^st under electron microscope.
Tobacco mosaic virus (TMV) is a positive-sense single-stranded RNA virus species in the genus. The infection causes characteristic patterns, such as "mosaic"-like mottling and discoloration on the leaves.
TMV was the first virus to be discovered. It is the first pathogen identified as a virus. The virus was crystallized by W. M. Stanley. It has a similar size to the largest synthetic molecule, known as PG5.