Effective Atomic Number in [Co(NH3)6]Cl3
Effective atomic number (EAN) is a concept that helps in determining the stability of coordination complexes. In [Co(NH3)6]Cl3, cobalt is surrounded by six ammonia ligands and three chloride ions.

Calculation of Effective Atomic Number
To calculate the EAN of [Co(NH3)6]Cl3, we need to consider the charges of the ligands and the central metal ion. In this case, cobalt has a charge of +3 (since it is in a +3 oxidation state) and each ammonia ligand has a charge of 0, while each chloride ion has a charge of -1.

Calculations:
- Cobalt: +3
- Ammonia ligands: 6 x 0 = 0
- Chloride ions: 3 x (-1) = -3
Adding these charges together, we get:
EAN = +3 + 0 - 3 = 0

Explanation
The EAN of 0 suggests that the coordination complex is stable since the total charge around the central metal ion is equal to its oxidation state. This indicates that the ligands are effectively neutralized by the central metal ion, leading to a stable complex.
In [Co(NH3)6]Cl3, the coordination number of cobalt is 6 and the complex has a total charge of +3, which is balanced by the charges of the ligands. This balanced charge distribution contributes to the stability of the complex.
In conclusion, the effective atomic number of [Co(NH3)6]Cl3 is 0, indicating a stable coordination complex where the ligands effectively neutralize the charge on the central metal ion.