Resolution Limit of Light Microscopes Steps:

• Recall that light microscopes resolve features down to ~200 nm (0.2 μm) due to visible light wavelength (400–700 nm).
• Convert all sizes to nanometers: A = 200,000 nm, B = 2 nm, C = 8 nm, D = 20 nm.
• Compare each to the 200 nm limit: only sizes ≥200 nm are visible.
• Identify the largest feature exceeding the limit.

Why A is correct:

• Paramecium cell at 200 μm (200,000 nm) far exceeds the 200 nm resolution, making it clearly visible under natural light.

Why the others are wrong:

• B: DNA at 2 nm is below 200 nm, requiring electron microscopy.
• C: Phospholipid bilayer at 8 nm is below 200 nm, not resolvable.
• D: Ribosome at 20 nm is below 200 nm, invisible with light.

Final answer: A