We are given a graph and we are asked to determine the type of function.
We notice that the graph is a line, therefore, it must be of the form:

Where "m" is the slope and "b" is the y-intercept.
The y-intercept "b" is the point where the line crosses the y-axis since from the graph we notice that the line crosses the y-axis at y = 0, we have:

Also, we notice that the point:

Is part of the line, therefore, we can substitute in the equation and we get:

Therefore, the slope is 1. Substituting we get:

Therefore, the right answer is identity y = x.