Isomers of [Co(NH3)4Cl(NO2)]

There are several types of isomers that can be formed for the coordination compound [Co(NH3)4Cl(NO2)]. Isomers are compounds that have the same molecular formula but differ in the arrangement of atoms or groups in space. In this case, we need to consider the possible isomers for the coordination sphere, which includes the central cobalt atom and its surrounding ligands.

Coordination Number and Geometry
The coordination number of cobalt in this complex is 6, as it is surrounded by six ligands - four ammonia molecules (NH3), one chloride ion (Cl), and one nitrate ion (NO2). The geometry of this complex is octahedral, as the six ligands are arranged around the cobalt ion in a symmetrical manner.

Possible Isomers
To determine the number of isomers, we need to consider the different ways in which the ligands can be arranged around the central cobalt atom. Let's consider each possibility:

1. Cis-Trans Isomerism: In this type of isomerism, the arrangement of ligands can be cis or trans to each other. For [Co(NH3)4Cl(NO2)], the chloride and nitrate ligands can be either cis or trans to each other. Therefore, we have two possible isomers:
- Cis-[Co(NH3)4Cl(NO2)]
- Trans-[Co(NH3)4Cl(NO2)]

2. Geometrical Isomerism: In this type of isomerism, the arrangement of ligands can be different in terms of their positions in space. For [Co(NH3)4Cl(NO2)], the four ammonia ligands can be arranged in two different ways, resulting in two possible isomers:
- [Co(NH3)4Cl(NO2)] (ammonia ligands arranged in a plane)
- [Co(NH3)2(NO2)Cl2] (ammonia ligands arranged in a tetrahedral fashion)

Total Number of Isomers
By considering the above possibilities, we have a total of four isomers for [Co(NH3)4Cl(NO2)].

Therefore, the correct answer is '4'.