Unbalanced forces are acting on an object when there is a net force acting on it, meaning that the forces do not cancel each other out.
From the options provided, the situation that describes unbalanced forces 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 scenario, since one person is pushing and the other is pulling (in opposite directions), the forces do not cancel each other out completely, resulting in an unbalanced force on the tire.