What mass of oxygen is present in this sample of znco3, which contains 3.11×1022 o atoms?

The given compound is ZnCO3

So each mole of ZnCO3 will have three moles of Oxygen atoms

So if the number of oxygen atoms in the sample = 3.11×10^22

It means the moles of oxygen atoms = number of atoms / Na (avagadro's number)

moles of oxygen atoms = 3.11×10^22 / 6.023 X 10^23 = 0.0516 moles

Mass of oxygen atoms = moles X atomic mass = 0.0516 X 16 = 0.8256 g