The number of monodentate ligands in the complex ion is called?(a) effect atomic number (b) coordination number (c) primary valency (d) oxidation number

The number of monodentate ligands in a complex ion refers to the number of individual ligands that each donate one electron pair to the central metal ion. When all ligands in a complex are monodentate, this number is equal to the coordination number. The coordination number is defined as the total number of donor atoms directly bonded to the central metal atom or ion.

Let's evaluate the options:

• (a) Effective atomic number (EAN): This is the total number of electrons surrounding the central metal ion in a complex. It is calculated as (atomic number of metal) - (oxidation state) + (2 × coordination number). This is not simply the number of ligands.
• (b) Coordination number: This is the number of donor atoms directly attached to the central metal ion. If all ligands are monodentate, then the number of monodentate ligands is exactly the coordination number.
• (c) Primary valency: This refers to the oxidation state of the central metal ion.
• (d) Oxidation number: This is the same as primary valency, representing the charge on the central metal ion.

Therefore, the most appropriate term for the number of monodentate ligands in a complex ion is the coordination number, assuming these are the only ligands present or referring to their contribution to the coordination sphere.

The correct answer is (b) coordination number.