Unbalanced forces act on an object when the total force acting on the object is not zero. In the scenarios provided, the situation in which unbalanced forces are acting on the tire is:
"Two people stand on the same side of a large tire. One person pushes the tire and the other pulls the tire with equal force."
In this case, one force is applied in the direction of pushing, and the other force is applied in the opposite direction of pulling. Since they are acting in opposite directions but with equal magnitude, the net effect is an unbalanced force.