Final answer:
The element with 20 neutrons that is a major component of teeth and bones is calcium. It's crucial for bone density, muscle function, and various other physiological processes.
Step-by-step explanation:
The element that has 20 neutrons and is found in your teeth and bones is calcium. Calcium is essential not only to provide hardness to bones and teeth but also plays critical roles in the body such as enabling muscle contraction, blood coagulation, and serving as a messenger in nerve transmissions. It's one of the most abundant minerals in the human body and very important for overall health. Among the options provided (Calcium, Iron, Potassium, Sodium), calcium is the correct answer as it is the only alkaline earth metal listed and typically has 20 neutrons in its most common isotope, Calcium-40.