To find a function is one to one we have to perform vertical and horizontal line test
And if it clears the test then it would be one to one
Graph 1 doesn't clears horizontal line test as if we draw a horizontal line it will cut the curve two times with same value of Y
Same is the case with Graph 2 , as if we draw a horizontal line it will cut the graph at two same values!
So graph2 also eliminated!
Graph 3 is an ellipse along y axis so it so the horizontal line cuts the ellipse two times with same values of y and if we draw a vertical line then, also it will cut the ellipse two times with same value of x
So option 3 eliminated!
But in Graph 4 if we draw a horizontal or vertical line it will cut the given points with same value of y or x