Understanding Turnbull's Blue
Turnbull's Blue is a complex compound primarily composed of iron and cyanide ions. It is critical in various applications, including dyeing and analytical chemistry.

Composition of Turnbull's Blue
- Turnbull's Blue is scientifically known as **Ferrous Ferricyanide**.
- The chemical formula can be represented as **Fe3[Fe(CN)6]2**, which indicates that it consists of both ferrous (Fe²⁺) and ferricyanide ([Fe(CN)6]³⁻) ions.

Formation Process
- This compound is formed when ferrous ions react with ferricyanide ions in a solution.
- The blue color arises from the electronic transitions within the iron centers, specifically due to the presence of the ferricyanide ion.

Properties of Turnbull's Blue
- It exhibits a vibrant blue color, which is a characteristic feature of many ferrous-ferricyanide complexes.
- It is relatively stable and can be used as a pigment in various applications.

Applications
- Turnbull's Blue is utilized in **art and dyeing**, where its intense color is favorable.
- In **analytical chemistry**, it serves as a colorimetric reagent for detecting ferrous ions.

Clarification of Other Options
- **Ferricyanide**: Refers to the ion [Fe(CN)6]³⁻, not a complete compound.
- **Ferrous Ferrocyanide**: Also known as Prussian Blue, which contains ferrous ions and ferrocyanide.
- **Ferrous Cyanide**: This term usually refers to a less stable compound, not Turnbull's Blue.
In conclusion, Turnbull's Blue is correctly identified as **Ferrous Ferricyanide** due to its unique composition and properties.