Question:
Which one of the following complexes is violet in colour?
Correct Option: 4,
Solution:
(1) $\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4} \rightarrow$ Pale yellow solution
(2) $\left[\mathrm{Fe}(\mathrm{SCN})_{6}\right]^{4} \rightarrow$ Blood red colour
(3) $\mathrm{Fe}_{4}\left[\mathrm{Fe}\left(\mathrm{CN}_{6}\right)\right]_{3} \cdot \mathrm{H}_{2} \mathrm{O} \rightarrow$ Prussian blue
(4) $\left[\mathrm{Fe}(\mathrm{CN})_{5} \mathrm{NOS}\right]^{4} \rightarrow$ Violet colour