Answer
Options b) & d) have 3 significant figures.
Work Step by Step
a). 305.0 cm has 4 significant figures. Since zeros in between and at the end of the number after decimal are significant.
b). 0.0500 mm has 3 significant figures. Zeros in front have no significance.
c). 1.00081 has 6 significant figures as zeros in between numbers have significance.
d). $8.06\times 10^{4} m^{2}$ has 3 significant figures.
So, b) and d) have 3 significant figures.
