Viruses are visible under a light microscope.

• A. True
• B. False
• C. Only under electron microscopy
• D. Never visible under any microscope

Answer: (B)

The main idea here is understanding the size you can resolve with a microscope. Most viruses are only 20–300 nanometers in diameter, which is well below the resolving power of a light microscope (about 200 nanometers). Because of that diffraction limit, viral particles are not visible under standard light microscopy. To actually see virions, you need electron microscopy, which provides the nanometer-scale resolution required. So the statement is false: viruses are not visible under a light microscope, and visualization typically requires electron microscopy.