Answer : 2. "Knoll and Ruska"
Explanation :

The electron microscope was co-invented by Max Knoll and Ernst Ruska in 1931. This revolutionary microscopy technology uses a beam of electrons to achieve much higher resolution than that of traditional light microscopes, allowing scientists to visualize extremely small structures, including individual cells and even subcellular components. The invention of the electron microscope significantly advanced the field of microscopy, enabling researchers to explore the microscopic world in unprecedented detail.