Diffraction limit of visible light in optical microscopy

Steps:

• Daylight provides visible light with average wavelength λ ≈ 550 nm.
• Resolution is governed by Abbe's formula: d ≈ λ / (2 NA), where NA is numerical aperture.
• For a typical 40x objective, NA ≈ 1.0 (high-dry or oil), yielding d ≈ 275 nm, but standard light microscope resolution is 200 nm.
• Eyepiece (10x) affects magnification, not resolution.

Why B is correct:

• Abbe's criterion limits visible light microscopes to ~200 nm resolution due to diffraction of wavelengths around 500 nm.

Why the others are wrong:

• A: 0.2 nm requires electron microscopes with much shorter wavelengths.
• C: 100 μm is too low, comparable to naked-eye limits.
• D: 400 μm is even coarser, unsuitable for microscopic detail.

Final answer: B