What elements are in hydroxyapatite, Cas(PO),OH, a major compound in human bones and teeth? A) carbon, potassium, oxygen, hydrogen B) calcium, phosphorous, oxygen, hydrogen C) carbon, phosphorous, oxygen, helium D) calcium, phosphorous, oxygen, helium E) carbon, potassium, oxygen, helium
The correct answer and explanation is :
The correct answer is:
B) calcium, phosphorous, oxygen, hydrogen
Explanation (Approx. 300 words):
Hydroxyapatite is a naturally occurring mineral form of calcium apatite with the formula often written as Ca₅(PO₄)₃(OH), but commonly presented as Ca₁₀(PO₄)₆(OH)₂ to reflect the crystal unit. This compound is the main inorganic component of human bones and teeth, making up about 70% of bone by weight and around 90% of tooth enamel.
Let’s break down the formula to identify its elements:
- Ca stands for calcium
- PO₄ is the phosphate group, which contains phosphorus (P) and oxygen (O)
- OH is the hydroxide group, which contains oxygen (O) and hydrogen (H)
From this, we can see that hydroxyapatite contains calcium (Ca), phosphorus (P), oxygen (O), and hydrogen (H)—which exactly matches Answer B.
Let’s also review why the other answer choices are incorrect:
- A (carbon, potassium, oxygen, hydrogen): Carbon and potassium are not part of hydroxyapatite.
- C (carbon, phosphorous, oxygen, helium): Helium is an inert gas and not found in hydroxyapatite; carbon is also absent from its formula.
- D (calcium, phosphorous, oxygen, helium): Correct elements except for helium, which is not present.
- E (carbon, potassium, oxygen, helium): None of these elements, except oxygen, are found in hydroxyapatite.
Hydroxyapatite’s strong and stable crystalline structure gives bones and teeth their rigidity and hardness. It’s also biocompatible, which is why synthetic hydroxyapatite is often used in bone grafts and dental implants. Understanding its elemental composition helps in medical, dental, and materials science fields.