The coefficient of any substance in a chemical equation indicates the number of moles of that substance which are present. We can see from its chemical formula that tetraiodine nonaoxide contains four iodine atoms and nine oxygen atoms. If the coefficient is two, then the total iodine atoms will be eight and the total oxygen atoms will be 18. Because the law of conservation of mass holds, an equal amount must be accounted for on the other side of the chemical equation. Therefore, the first option is correct.
