The instantaneous speed is always positive as it is the magnitude of the velocity at an instant, so it is positive during t = 5 s to t =10 s. 

For t = 0 s to t = 5 s, the motion is uniform and x-t graph has positive slope. 

So, the velocity and average velocity, instantaneous velocity and instantaneous speed are equal and positive. During t = 0 s to t = 5 s, the slope of the graph is positive, hence the average velocity and the velocity both are positive. 

During t = 5 s to t =10 s, the slope of the graph is negative, hence the velocity is negative. Since, there is a change in sign of velocity at t = 5 s, so the car changes its direction at this instant. Hence, option (a) is incorrect, while all others are correct.