When an object is travelling in a circular path it has an acceleration called centripetal acceleration, even if it is moving with uniform speed. This acceleration is attributed to the object due to change in the direction of velocity at every instant during the motion.
The direction of the velocity of the object is tangent to the circular path at every instant and if the object beaks free of the circular motion, such as breaking of the string, then it will go in the direction tangent to the circle at that instant. Hence, the diagram that best shows the direction ball will travel is:
