Which of the following coordinate complexes contains one or more...

Let us analyze the ligands present in the coordination sphere of each complex:

Potassium trioxalatoaluminate(III): $K_3[Al(C_2O_4)_3]$ contains oxalato ligands (C_2O_4^{2-}$), which are anionic.<br><br>Pentaammineaquacobalt(III) iodide:$[Co(NH_3)_5(H_2O)]I_3$contains ammine (NH_3$) and aqua (H_2O$) ligands, both of which are neutral molecules.<br><br>Sodium hexanitrocobaltate(III):$Na_3[Co(NO_2)_6]$contains nitro ligands (NO_2^{-}$), which are anionic.

Hexacyanoferrate(II) ion: $[Fe(CN)_6]^{4-}$ contains cyano ligands (CN^{-}$), which are anionic.<br><br>Thus, pentaammineaquacobalt(III) iodide is the only complex containing neutral ligands in its coordination sphere.<br><br>Answer: Pentaammineaquacobalt(III) iodide$