Magnification formula: image size divided by actual size

Steps:

• Measure the length of line X-Y in the micrograph image (typically in mm; here, 63 mm).
• Convert actual chloroplast length to consistent units: 10 μm = 0.01 mm.
• Apply magnification formula: M = image length / actual length = 63 mm / 0.01 mm.
• Calculate: 63 / 0.01 = 6300, so magnification is ×6300.

Why D is correct:

• Matches the formula M = (measured image length in mm) / (actual length in mm), yielding ×6300 for a 63 mm image line and 0.01 mm actual size.

Why the others are wrong:

• A: ×6.3 underestimates by factor of 1000, ignoring μm-to-mm conversion.
• B: ×63 underestimates by factor of 100, treating actual as 1 mm instead of 0.01 mm.
• C: ×630 underestimates by factor of 10, from partial unit mismatch.

Final answer: D