cm and mm are both units used to measure length
the starting measurement is 0.0510 cm
The number of significant figures are the number of digits starting from the first non zero digit from left to right
in 0.0510 the first non zero digit from the left is 5
then there are 3 significant figures. The last zero too is significant
1 cm is equivalent to 10 mm
therefore 0.0510 cm = 10 mm/cm x 0.0510 cm = 0.510 mm
the answer 0.510 too has 3 significant figures, same as 0.0510 cm
correct answer is B, 0.510 mm
