Which of the following is not equal to 0.1 centimeters?
a)0.1 kilometers (km)
b)0.001 meters (m)
c)10 millimeters (mm)
d)1000 micrometers (µm)

Best way to answer this problem is to convert all units into SI unit (meter), then compare the output:

0.1 cm = 0.1 x 10^-2 = 1 x 10^-3 m
0.001 m = 1 x 10^-3 m
0.000001 Km = 0.000001 x 10^3 = 1 x 10^-3 m
10 mm = 10 x 10^-3 = 1 x 10^-2 m
1000 µm = 1000 x 10^-6 = 1 x 10^-3 m

Comparing the results, we find that 10 mm is not equal to 0.1 cm.
The answer is (c)