Magnification and unit conversion to find image size Steps:

• Actual diameter = 2.5 μm.
• Magnified diameter = 2.5 μm × 50,000 = 125,000 μm.
• Convert μm to mm: divide by 1,000 (1 mm = 1,000 μm), so 125,000 / 1,000 = 125 mm.
• Express in scientific notation: 125 mm = 1.25 × 10² mm. Why C is correct:
• Magnification formula (image size = actual size × magnification factor) with proper unit conversion (1 μm = 10^{-3} mm) yields exactly 1.25 × 10² mm. Why the others are wrong:
• A: Overestimates by factor of 100, as if μm to mm conversion divided by 10 instead of 1,000.
• B: Overestimates by factor of 10, as if μm to mm conversion divided by 100.
• D: Underestimates by factor of 10, as if actual diameter was 0.25 μm instead of 2.5 μm. Final answer: C