Which of the following statements is incorrect?

• A

  In $\mathrm{K}_{4}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$ the ligand has satisfied both primary and secondary valencies of ferrous ion.
• B

  In $\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{SO}_{4}$, the ligand has satisfied only the secondary valency of copper.
• C

  In $\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, the ligand has satisfied only the secondary valency of ferric ion.
• Correct answer
  D

  In $\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, the ligand has satisfied both primary and secondary valencies of ferric ion.

Solution

In $\mathrm{K}_{3}\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]$, the ligand has satisfied both primary and secondary valencies of ferric ion. The $+3$ charge of ferric ion is satisfied by negative charge on cyanide ion. The coordination sphere's secondary valency is satisfied by six cyanide ligands.

Hence, the correct answer is option: 'D'.