This is a bacteria without cell wall

The correct option is mycoplasma.

Step-by-step Explanation:

1. Understanding Mycoplasmas:
Mycoplasmas are a unique group of bacteria that completely lack a cell wall surrounding their cell membrane. Because they do not have a rigid peptidoglycan cell wall, they are naturally resistant to many common antibiotics (such as penicillin) that target cell wall synthesis.

2. Analyzing the Options:
• virus: Viruses are non-cellular, infectious agents consisting of genetic material (DNA or RNA) wrapped in a protein coat (capsid). They are not classified as bacteria.
• mycoplasma: These are indeed bacteria that lack a cell wall. They are the smallest known free-living organisms and can survive without oxygen.
• cyanobacteria: Also known as blue-green algae, cyanobacteria are photosynthetic bacteria that possess a distinct, rigid cell wall.
• viroid: Viroids are sub-viral plant pathogens composed solely of a short strand of circular, single-stranded RNA without any protein coat or cellular structure. They are not bacteria.

Therefore, among the given choices, the bacteria that do not possess a cell wall are mycoplasmas.