Final answer:
In a 0.78 mol sample of CaCO₃, there are approximately 4.709 x 10^23 atoms of oxygen.
Step-by-step explanation:
In a sample of CaCO₃, there is one atom of carbon, three atoms of oxygen, and one atom of calcium. Since the molar mass of CaCO₃ is approximately 100 g/mol, and there are 0.78 mol of CaCO₃ in the sample, we can calculate the number of atoms of oxygen by multiplying the number of moles by Avogadro's number (6.022 x 10^23).
Number of atoms of oxygen = 0.78 mol x 6.022 x 10^23 atoms/mol
Number of atoms of oxygen = 4.709 x 10^23 atoms