14. The diameter of carbon atom is about 3.4 x 10-7 millimeter. Is it more appropriate to report the diameter of carbon atom as 3.4 x 10-7 millimeter or 3.4 x 10-13 kilometer? Explain your reasoning.
I

  it depends

Step-by-step explanation:

I like to choose the units to be compatible with the use of the number.

In Engineering, we often choose units so the number itself is between 1 and 1000. Here, that means 3.4×10^-7 mm would be better expressed as 3.4 angstroms or 340 pm (picometers). (The purpose of SI prefixes is to facilitate this way of representing metric measures.)

If you're comparing the length to something measured in km, then the representation as 3.4×10^-13 km might be the most useful

If you're comparing the distance to something measured in mm, then 3.4×10^-7 mm would be more appropriate than 3.4×10^-13 km.