The subscripts to the right of each atom in the molecular formular indicate the number of atoms of that element in one molecucule.
That means, for example, that in one molecule of C2H5OH there are 2 atoms of C, 6 atoms of H and 1 atom of O.
So, 1 mol of ethanol, C2H5OH contains 1 mol of atoms of O; 1 mol of formic acid, HCO2H contains 2 moles of atoms of O; and 1 mol of water, H2O contains 1 mol of atoms of O.
Answer: So, of the three compounds given, formic acid, HCO2H, contains the greatest number of moles of oxygen atoms.
