Bones are composed mostly of __________.

• A. vitamins
• B. calcium
• C. magnesium
• D. cartilage

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the composition of bones. Bones are primarily made up of a mineralized matrix that provides strength and rigidity.
2. Step 2: Recall that the primary mineral in bones is calcium, which is stored in the form of hydroxyapatite crystals (Ca₁₀(PO₄)₆(OH)₂). This mineral gives bones their hardness.
3. Step 3: Recognize that while magnesium and other elements are present in bones, they are in much smaller amounts compared to calcium.
4. Step 4: Note that cartilage is a flexible connective tissue found in joints and other parts of the body, but it is not the primary component of bones.
5. Step 5: Conclude that the correct answer is calcium, as it is the most abundant and essential component of bone structure.