The correct option is A Mitochondria
Mitochondria have maximum number of biocatalysts in cell, it ranges from 0.5 to 1.0 μm in diameter. A considerable variation can be seen in the structure and size of this organelle. Unless specifically stained, they are not visible. These structures are described as "the power house of the cell" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. These biological reactions need many bio catalytic reactions, in the presence of enzymes.