Virus Size vs. Microscope Resolution Limit

Steps:

• Convert units: 0.25 μm = 250 nm (resolution limit, smallest resolvable size).
• Compare Norovirus (30 nm) to 250 nm: 30 nm < 250 nm, too small to resolve.
• Compare Mimivirus (400 nm) to 250 nm: 400 nm > 250 nm, large enough to detect as a distinct object.
• Light microscopes cannot visualize structures below their resolution limit due to diffraction of visible light.

Why B is correct:

• Resolution limit (Abbe diffraction limit) requires objects ≥250 nm for detection; Norovirus is sub-resolution, Mimivirus exceeds it.

Why the others are wrong:

• A: Mimivirus (400 nm) exceeds 250 nm, so detectable.
• C: Norovirus (30 nm) is below 250 nm, undetectable.
• D: Norovirus is too small to detect.

Final answer: B