Final answer:
The normal force's reaction is the weight of the object due to gravity. The action-reaction pair for the normal force is the weight of the object and the normal force exerted by the surface, answering 'a. weight and force applied'.
Step-by-step explanation:
The action-reaction pair for the normal force (Fnormal) is the contact force that surfaces exert to support the weight of objects, and it's directed perpendicularly to the surface. This force is essential to counteract the weight of an object due to gravity, which pulls it downwards. In the context of Newton's third law, which states that for every action there is an equal and opposite reaction, the action-reaction pair for the normal force is the weight of the object (the action) and the normal force exerted by the surface (the reaction). The correct answer to this question is therefore 'a. weight and force applied'. When an object is placed on a surface, such as a table, the table sags slightly like a trampoline, then applies an equal and opposite normal force to support it, preventing it from falling. The magnitude of the normal force is equal to the magnitude of the object's weight, assuming there's no other vertical force acting on the object.