For a reaction X → Y, the graph of the product concentration (x) versus time (t) came out to be a straight line passing through the origin. Hence the graph of –d[X]/dt and time would be:

If the product concentration is x
For a zero-order reaction
xt = k
Thus, the graph would be a straight line passing through the origin. So the given information is for a zero-order reaction. For a zero-order reaction, the rate of reaction is constant. Thus, the plot of rate vs time i.e., –d[X]/dt vs time will be a straight line parallel to the x-axis