The coordination complex that contains a neutral ligand among the given options is: Option A: Pentacarbonyl iron(0), which has the formula Fe(CO)5 Ligands can be neutral molecules or anions that donate a pair of electrons to the metal center to form coordinate bonds. Carbonyl (CO) is a common example of a neutral ligand, as it contains a carbon atom triple-bonded to an oxygen atom and has a lone pair of electrons that can be donated to a metal atom. In the complex Fe(CO)5, the iron atom is surrounded by five carbonyl ligands, all of which are neutral. Option B: Trioxalatocobaltate(III) ion contains oxalate ligands (C2O42−), which are anionic. Option C: Sodium hexanitrocobaltate(III), Na3[Co(NO2)6], contains nitro (NO2−)ligands, which are also anionic. Option D: Tetracyanonickelate(II) ion, [Ni(CN)4]2−, contains cyanide ligands (CN−), which are anionic as well. Hence, the complex with a neutral ligand is Option A: Pentacarbonyl iron(0).