The compound must contain at least one oxygen atom
So, a minimum of 1 g atom of oxygen will be present in 1 g molecule i.e., 1 mole of the compound.
If M is the mol. wt. of the compound then since 16 is the atomic mass of oxygen so minimum of 16 g of oxygen will be present in M g of the compound
Thus, % of oxygen = 16 / M × 100
or 3.2 = 1600 / M or M = 500
