To determine which mapping diagram shows a relation that is not a function, you would need to look for instances where a single element in the domain (input) is associated with more than one element in the range (output).
In a function, each input must have exactly one output. If you can identify a domain value that maps to multiple range values in any of the diagrams, that would indicate it is not a function.
Since the descriptions provided are identical and do not include visual representations, I am unable to determine which specific mapping diagram shows a relation that is not a function. Please provide more details or describe how the domain and range elements are connected in each diagram for a more accurate assessment.