Answer:
64 g/mol
Step-by-step explanation:
In one molecule of FeSO4, we notice that we have 4 atoms
Hence, we can say that the molar mass of Oxygen in 1 unit/molecule of FeSO4 is 4 times the molar mass of Oxygen
Molar mass of Oxygen atom (O) = 16 g / mol
Molar mass of Oxygen in FeSO4 = 16 * 4 g / mol
Molar mass of Oxygen in FeSO4 = 64 g / mol