Colour of [Ag(NH3)2 ] Cl
Ag(NH3)2 ] Cl is a coordination complex consisting of a central silver ion bonded to two ammonia ligands and one chloride ion. The colour of this complex can be explained by its electronic structure and the absorption of light.

Coordination Complex
In this complex, the central silver ion Ag+ is surrounded by two ammonia ligands (NH3) and one chloride ion (Cl-). The ammonia ligands act as Lewis bases, donating electron pairs to the silver ion, forming coordinate covalent bonds.

Electronic Structure
The colour of a coordination complex is determined by the electronic transitions that occur when the complex absorbs light. In the case of [Ag(NH3)2 ] Cl, the silver ion has d^10 electronic configuration, which means there are no d-d transitions. However, the complex can still absorb light in the visible region due to ligand-to-metal charge transfer (LMCT) transitions.

Colour Explanation
The colour of [Ag(NH3)2 ] Cl is typically pale yellow. This colour arises from the absorption of light in the visible region due to LMCT transitions from the ammonia ligands to the silver ion. The presence of the chloride ion also affects the colour by altering the energy levels involved in the electronic transitions.
In conclusion, the pale yellow colour of [Ag(NH3)2 ] Cl is a result of the electronic structure of the complex and the absorption of light due to LMCT transitions.