Final answer:
The correct answer is 'c. 12 N exerted by the book on the hand.' This is due to Newton's third law, which states that for every action there is an equal and opposite reaction, meaning the book exerts the same force exerted by the hand, but directed downward.
Step-by-step explanation:
Understanding Newton's Third Law in Context
When one's hand exerts an upward force of 12 N on a book that weighs 10 N, we need to determine the reaction to the force of the hand on the book. According to Newton's third law of motion, for every action, there is an equal and opposite reaction. Therefore, if the hand exerts 12 N upward, the book exerts the same force, but in the opposite direction, down on the hand. This means the correct answer to the question - 'The reaction to the force of the hand on the book' - is c. 12 N exerted by the book on the hand.
The reaction force is not the weight of the book, which is the gravitational force that Earth exerts on it, nor is it the net force difference. This reaction force is due to the direct interaction between the hand and the book, as described by Newton's third law.