The molecule [Co(en)2Cl(NO2)] contains a cobalt (Co) atom bonded to two ethylenediamine (en) ligands, one chloride (Cl) ligand, and one nitro (NO2) ligand. To determine the total number of isomers possible for this molecule, we need to consider the different possible arrangements of the ligands around the central cobalt atom.

1. Identify different types of isomers:
There are several types of isomers that can be formed depending on the arrangement of ligands around the central metal atom:
- Geometric isomers: These isomers arise due to the restricted rotation around a bond, resulting in different spatial arrangements of ligands.
- Optical isomers: These isomers are non-superimposable mirror images of each other and arise when the central metal atom is chiral or the ligands are chiral.

2. Determine the possible geometric isomers:
In [Co(en)2Cl(NO2)], the en ligands can be either cis or trans to each other. This means that the two en ligands can be arranged in one of two ways:
- cis arrangement: The en ligands are adjacent to each other.
- trans arrangement: The en ligands are opposite to each other.

3. Determine the possible optical isomers:
For a molecule to exhibit optical isomerism, it needs to be chiral. In [Co(en)2Cl(NO2)], the presence of the en ligands makes the molecule chiral. Therefore, there can be two possible optical isomers: one with clockwise rotation (R) and one with counterclockwise rotation (S).

4. Calculate the total number of isomers:
To determine the total number of isomers, we multiply the number of possible geometric isomers by the number of possible optical isomers:
Total number of isomers = Number of geometric isomers * Number of optical isomers
Total number of isomers = 2 (cis and trans) * 2 (R and S)
Total number of isomers = 4

However, it is important to note that the given correct answer is '6'. This suggests that there may be additional factors or arrangements that need to be considered, which are not explicitly mentioned in the question. Without further information, it is not possible to determine the exact reasoning behind the correct answer of '6'.