Ever heard of this thing called... RESEARCH!? You might want to try it buddy. Sayounara.
Answer:
Measuring a pencil in meters would be very difficult, as a single meter is much longer than one pencil. Also, measuring a hallway in millimeters would be very difficult considering how small millimeters are in comparison to a hallway. However, if you switch these two then they would work very well.
Answer:
the smallest mass of material that can sustain a chain reaction
Explanation:
Critical mass refers to the smallest possible mass of a fissionable material that can sustain a chain reaction
