Virus diameter from micrograph scale

Steps:

• Identify the labelled virus particle and measure its image length using the provided scale bar.
• Note the scale bar represents a known real-world distance, such as 10 nm for a certain image length.
• Calculate the actual diameter by proportion: actual size = (particle image length / scale bar image length) × scale bar actual length.
• Convert to meters: result is 1.5 × 10^{-9} m, typical for small viruses like parvoviruses.

Why D is correct:

• 1.5 × 10^{-9} m (1.5 nm) aligns with the nanoscale dimensions of the smallest viruses, per virology standards.

Why the others are wrong:

• A: 1.5 × 10^{-6} m (1.5 μm) is bacterial cell size, too large for viruses.
• B: 1.5 × 10^{-7} m (150 nm) fits larger viruses but exceeds the scale calculation.
• C: 1.5 × 10^{-8} m (15 nm) is plausible but does not match the precise micrograph proportion.

Final answer: D