Which of the following statement is incorrect?

In K₃[Fe(CN)₆] the ligand has satisfied only the secondary valency of ferric ion

The correct answer is (b) In \(K_3[Fe(CN)_6]\), the ligand has satisfied only the secondary valency of ferric ion.

Explanation:
In \(K_3[Fe(CN)_6]\), the coordination number of the ferric ion (\(Fe^{3+}\)) is 6, and it is surrounded by six cyanide ligands (\(CN^-\)). Each cyanide ligand donates one pair of electrons to the ferric ion, forming a coordinate bond. Cyanide (\(CN^-\)) is a strong field ligand, and it causes the splitting of the d-orbitals of the ferric ion, leading to the formation of a low-spin complex.

The term "primary valency" refers to the oxidation state or charge of the central metal ion. In this case, the ferric ion (\(Fe^{3+}\)) has a primary valency of +3.

The term "secondary valency" refers to the coordination number or the number of ligands coordinated to the central metal ion. In this case, the coordination number of the ferric ion is 6, and it is satisfied by six cyanide ligands, each donating one electron pair.

Therefore, statement (b) is incorrect because the ligand (\(CN^-\)) in \(K_3[Fe(CN)_6]\) satisfies both the primary valency (+3) and the secondary valency (coordination number 6) of the ferric ion.