In an experiment, the length of an object is measured to be 6.50 cm. This measured value can be written as 0.0650 m. The number of significant figures on 0.0650 m is
3
Significant figures are the digits that carry the precision of a measurement. Changing the unit cannot change the precision, so the number of significant figures must stay the same. The rules: leading zeros only locate the decimal point and are not significant; trailing zeros after a decimal point are significant.
Step 1 — In 0.0650 m, the zeros before 6 ("0.0") are leading zeros and are not significant.
Step 2 — The digits 6 and 5 are significant, and the final 0, written after the decimal point, is also significant.
Step 3 — So 0.0650 m has three significant figures (6, 5, 0), exactly as 6.50 cm does.
Four or five would wrongly count the leading zeros, which only fix the position of the decimal point, while two would drop the trailing zero that records the measured precision.
3 option is correct.
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