Which one of the following is smallest cell?

Mycoplasma (specifically Mycoplasma gallisepticum) are the smallest known living cells, measuring only about 0.1 to 0.3 micrometers in diameter. They are unique because they lack a cell wall, allowing them to survive without oxygen and take on various shapes.
For comparison:
• Red blood cells: Around 6–8 micrometers.
• White blood cells: Around 10–15 micrometers.
• Amoeba: Much larger single-celled organisms, often ranging from 200 to 500 micrometers.