Functional isomerism is possible with molecular formula

$$\begin{gathered} \mathrm{I}) {\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{O}}_2 \\ \mathrm{II}) {\mathrm{C}}_3{\mathrm{H}}_7\mathrm{Br} \\ \mathrm{III}) {\mathrm{C}}_2{\mathrm{H}}_6\mathrm{O} \\ \mathrm{IV}) {\mathrm{CH}}_5\mathrm{N} \end{gathered}$$