Which of the following statements is incorrect?
a.In K₃[Fe(CN)₆], the ligand has satisfied only the secondary valency of ferric ion.
b.In K₃[Fe(CN)₆], the ligand has satisfied both primary and secondary valencies of ferric ion.
c.In K₄[Fe(CN)₆], the ligand has satisfied both primary and secondary valencies of ferrous ion.
d.In [Cu(NH₃)₄]SO₄ the ligand has satisfied only the secondary valency of copper.