SOLUTION
To identify or determine which relation in the graph is a function, we use the vertical line test.
The vertical line test explains that If we can draw any vertical line that intersects a graph more than once, then the graph does not define a function because that x-value has more than one output. A function has only one output value for each input value.
Hence, from the explanation above, we cam see that
Graph 1 is a Function
Graph 2 is a Function
Using similar approach
Graph 3 is not a function
Graph 4 is not a function