The formula for the green complex formed when aqueous iron(II) is added to potassium hexacyanochromate is K3[Fe(Cr(CN)6)2].

Explanation:

1. Introduction:
When aqueous iron(II) is added to potassium hexacyanochromate, a red-colored complex is formed initially. This complex undergoes a change in color to green upon heating. This change in color indicates a structural rearrangement of the complex and the formation of a new complex.

2. Formation of the red complex:
The initial reaction involves the formation of a red-colored complex. The hexacyanochromate ion (Cr(CN)6)^3- acts as a ligand and coordinates with the iron(II) ion (Fe^2+), forming a complex ion. The formula for this red complex is K3[Fe(Cr(CN)6)].

3. Structural rearrangement:
Upon heating, the red complex undergoes a structural rearrangement, resulting in a change in color to green. This rearrangement involves the formation of a new complex with a different structure.

4. Formation of the green complex:
The green complex is formed by the coordination of two hexacyanochromate ions with one iron(II) ion. The formula for this green complex is K3[Fe(Cr(CN)6)2]. This complex consists of one iron(II) ion coordinated with two hexacyanochromate ions.

5. Role of ligands:
The hexacyanochromate ion acts as a ligand in both the red complex and the green complex. It forms coordination bonds with the central iron(II) ion through its cyanide (CN) groups. The coordination of two hexacyanochromate ions in the green complex results in a more stable structure and a different color.

6. Color change:
The change in color from red to green is due to the difference in the electronic transitions that occur in the two complexes. The red complex absorbs light in the visible region, resulting in the appearance of a red color. In contrast, the green complex absorbs light of a different wavelength, leading to the perception of a green color.

In conclusion, the formula for the green complex formed when aqueous iron(II) is added to potassium hexacyanochromate is K3[Fe(Cr(CN)6)2]. The structural rearrangement of the red complex upon heating results in the formation of this green complex, which exhibits a different color due to the change in electronic transitions.