Which of the following can show both geometrical and optical isomerism?

[Fe(NH₃) (H₂O) (Py) (Br) (Cl) (OH)]

To determine whether a complex can exhibit both geometrical (cis-trans) and optical (enantiomeric) isomerism, we need to check for the presence of different ligands that can create isomeric forms.

(a) [Co(Ox)₃]^3–:- This complex has three bidentate oxalate ligands. Bidentate ligands can lead to geometrical isomerism if they can coordinate in different ways. However, oxalate ligands are not chiral, so optical isomerism is not possible. Incorrect.

(b) [Fe(NH₃)₄Cl₂]⁺:- This complex has four ammonia (NH₃) ligands and two chloride (Cl^-) ligands. The ammonia ligands can exist in cis or trans positions relative to each other, creating geometrical isomers. However, there are no chiral ligands, so optical isomerism is not possible. Incorrect.

(c) [Fe(NH₃)(H₂O)(Py)(Br)(Cl)(OH)] :- This complex has multiple different ligands: ammonia (NH₃), water (H₂O), pyridine (Py), bromide (Br^-), chloride (Cl^-), and hydroxide (OH^-). With this combination of ligands, it is possible to have both geometrical isomers (e.g., cis/trans isomers of ligands) and optical isomers if at least one of the ligands is chiral. The presence of pyridine (Py) suggests the potential for a chiral center, enabling optical isomerism. This complex can exhibit both geometrical and optical isomerism.

(d) [Co(NH₃)₃(NO₂)₃]:- This complex has three ammine (NH₃) ligands and three nitrito (NO₂^-) ligands. While the coordination geometry could potentially lead to geometrical isomers (cis-trans), neither NH₃ nor NO₂^- ligands are chiral. As a result, optical isomerism is not possible. Incorrect.

The correct answer is: (c) [Fe(NH₃)(H₂O)(Py)(Br)(Cl)(OH)]