All measures of variation are nonnegative in value for all sets of data. a. What does it

Question:

All measures of variation are nonnegative in value for all sets of data.
a. What does it mean for a value to be “nonnegative”?
b. Describe the conditions necessary for a measure of variation to have the value zero.
c. Describe the conditions necessary for a measure of variation to have a positive value.