Question

Intense blue colour of Prussian blue arises as a result of :

• A. Electron transfer between $Fe\left(II\right)$ and $Fe\left(I\right)$
• B. Electron transfer between $Fe\left(II\right)$ and $Fe\left(III\right)$
• C. $d-d$ transition of electron
• D. Ligand metal charge transfer

Answer 1

The correct option is B Electron transfer between $Fe\left(II\right)$ and $Fe\left(III\right)$

Option (B) is correct. Intense blue colour of Prussian Blue $KF{e}^{III}\left[F{e}^{II}\right(CN{)}_6]$ arises as a result of electron transfer between $Fe\left(II\right)$ and $Fe\left(III\right)$.

It absorbs certain wavelengths of visible light resulting from intervalence charge transfer and these transfers are often fully allowed, they give rise to intense colour. In this case, orange-red light is absorbed, and the reflected light appears blue.