Given the velocity-time graph of an object.
The slope of a velocity-time graph gives the acceleration of the object.
From the graph, we can see that the slope of the object is not zero. Hence there is an acceleration acting on the object.
From Newton's second law, the net force acting on an object is given by the product of the mass of the object and the acceleration acting on it.
Therefore, as the object has a net acceleration there is a net force acting on the object. Therefore the force is unbalanced.
We can see that the slope of the graph is increasing with time. Therefore the acceleration of the object and hence the force acting on the object is increasing over time.
Therefore the correct answer is option C.