To solve this problem, we need to determine the correct order of increasing field strength of ligands.$\newline$The field strength of ligands is determined by the spectrochemical series, which ranks ligands based on their ability to split the d-orbitals of a metal ion.$\newline$The spectrochemical series for some common ligands is as follows:$\newline$I$^- <$Br$^- <$S$^{2-} <$SCN$^- <$Cl$^- <$F$^- <$OH$^- <$C$_2$O$_4^{2-} <$H$_2$O$<$NH$_3 <$en$<$CN$^- <$CO$\newline$From this series, we can identify the order of field strength for the given ligands:$\newline$• $$SCN$^-$ is weaker than $$F$^- \newline$• $$F$^-$ is weaker than $$C$_2$O$_4^{2-} \newline$• $$C$_2$O$_4^{2-}$ is weaker than $$CN$^- \newline$Thus, the correct order of increasing field strength is:$\newline$SCN$^- <$F$^- <$C$_2$O$_4^{2-} <$CN$^- \newline$This corresponds to Option 4.