Phosphoric Acid Can Be Prepared by Reaction of Sulfuric Acid $\to$

Phosphoric acid can be prepared by reaction of sulfuric acid with "phosphate rock" according to the equation: Ca₃(PO₄) ₂ + 3H₂SO₄ $\to$ 3CaSO₄ + 2H₃PO₄
How many oxygen atoms are there in 1.75 ng of Ca₃(PO₄) ₂?

A) 3.40 $\times$ 10¹²
B) 1.36 $\times$ 10¹³
C) 8.43 $\times$ 10¹⁵
D) 2.72 $\times$ 10²²
E) 2.72 $\times$ 10¹³