Final answer:
The smallest distance at which two points can be resolved by light microscopy is 0.2 μm. This limitation is due to light diffraction and is the standard resolution for most light microscopes.
Step-by-step explanation:
The smallest distance two points can be separated and still resolved using light microscopy is about 0.2 μm (b). This is due to the limit imposed by the diffraction of light waves. Light microscopes typically used in a college biology lab can magnify up to approximately 400 times and have a resolution limit of 200 nanometers, which equates to 0.2 μm. Options like 20 nm, 2 μm, and 200 μm do not represent the practical limit of resolution for most light microscopes. Electron microscopes, on the other hand, can resolve much smaller structures with their higher magnification and resolution capabilities.