Chapter 7, Problem 56E

From the following list, identify each formula that could be an empirical formula. Write the empirical formulas of any compounds that are not already empirical formulas:

${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}\text{O}$; ${\text{Na}}_{\text{2}}{\text{O}}_{\text{2}}$; ${\text{C}}_{\text{2}}{\text{H}}_{\text{4}}{\text{O}}_{\text{2}}$; ${\text{N}}_{\text{2}}{\text{O}}_{\text{5}}$.