avogadros number was calculated by determining the number of atoms in\no 12.00 g of carbon - 12.\no 14.00 g…

Brief Explanations:

Avogadro's number ($N_A$) is defined as the number of atoms in 12.00 g of carbon - 12. One mole of any substance contains Avogadro's number of entities. The molar mass of carbon - 12 is 12 g/mol, so 12.00 g of carbon - 12 is exactly 1 mole and has $N_A$ atoms. Oxygen has a different molar mass and the given masses of oxygen do not define Avogadro's number. Also, 14.00 g of carbon - 12 is not the standard amount used to define Avogadro's number.

Answer:

12.00 g of carbon - 12.