Final answer:
Fluoride is the substance that stabilizes bones and makes teeth resistant to decay by forming fluorapatite, which is less soluble and strengthens both bones and teeth. So, the correct option is 3) Fluoride.
Step-by-step explanation:
The substance that stabilizes bones and makes teeth resistant to decay is fluoride. When added to drinking water, fluoride helps to prevent tooth decay by providing frequent and consistent contact with low levels of fluoride. It helps rebuild and strengthen the tooth's surface, or enamel, thus making the teeth more resistant to acid attacks. Furthermore, fluoride can displace the hydroxyl group in bone's hydroxyapatite crystals to form fluorapatite, which stabilizes and strengthens bone mineral density.