Considering graph I:
Graph I consists of a set of ordered pairs (x,y), Hence, it is a relation.
Look for any value(s) of x that have more than one corresponding value of y.
x=3 has more than one corresponding value of y, i.e., y=1 and y=3.
Each input (x) of Graph I does not have a unique output (y), as one input has two outputs, i.e., (3,1) and (3,3). Hence, Graph I is a relation, but not a function.
Considering graph II:
Graph II consists of a set of ordered pairs (x,y). Hence, it is a relation.
Look for any value(s) of x that have more than one corresponding value of y.
As the graph represents a straight line that is not vertical, there is no value of x that will have more than one corresponding value of y.
Each input (x) of Graph II has a unique output (y).
Hence, Graph II is a function.