Newton's Third Law of Motion states, "For every action, there is an equal and opposite reaction." This fundamental principle of physics explains the interaction of forces between two objects. Let's analyze the given options to determine which statement is incorrect regarding this law:

1. When one object exerts a force on another, the second object exerts an equal and opposite force back: This is a correct statement. According to Newton's third law, if object A exerts a force on object B, then object B will exert an equal and opposite force on object A.
2. The forces are equal in magnitude but opposite in direction: This is also a correct statement. The reciprocal forces described by Newton's third law always have the same magnitude but act in opposite directions.
3. The action and reaction forces act on the same object: This is the incorrect statement. Newton's third law explicitly states that the action and reaction forces act on two different objects, not on the same object.
4. The forces act simultaneously on two different objects: This is correct. The action and reaction forces are simultaneous and occur on two separate objects involved in the interaction.

In conclusion, the incorrect statement is: "The action and reaction forces act on the same object." This choice violates the very essence of Newton's third law, as the reaction force is always exerted by a different object than the one exerting the action force.