Of the following, which ligand does not posses the name suggested by IUPAC when it acts as a ligand in complex?

NH₃, ammonia

The correct answer is option 2. NH₃, ammonia.

Let us delve into the IUPAC nomenclature for ligands in coordination chemistry.

In coordination chemistry, ligands are molecules or ions that donate at least one pair of electrons to a central metal atom or ion to form a coordination complex. The IUPAC (International Union of Pure and Applied Chemistry) has specific rules for naming these ligands:

1. \(H_2O\), aqua: When water acts as a ligand, it is called "aqua." This term is derived from Latin, and it is the standardized name used in coordination chemistry.
   
2. \(NH_3\), ammonia: When ammonia acts as a ligand, the correct IUPAC name is "ammine." The term "ammine" specifically refers to ammonia when it is coordinated to a metal center. "Ammonia" is the name for the free molecule, not when it acts as a ligand.

3. CO, carbonyl: When carbon monoxide acts as a ligand, it is called "carbonyl." This name is derived from the term used in organic chemistry for the CO group, and it is standardized for coordination compounds.
   
4. \(F^-\), fluoro: When the fluoride ion acts as a ligand, it is called "fluoro." This follows the convention of using the "o" ending for anions when they act as ligands (e.g., "chloro" for \(Cl^-\), "bromo" for \(Br^-\), etc.).

The discrepancy in your provided names lies with \(NH_3\), ammonia. Here’s why:

\(NH_3\) as a ligand: When ammonia \((NH_3)\) coordinates to a metal ion, it is referred to as "ammine" (with two 'm's). This term distinguishes it from the free ammonia molecule. The reason behind this naming convention is to avoid confusion and to follow the systematic approach in naming complexes.

Example: Consider the complex \([Cu(NH_3)_4]^{2+}\). According to IUPAC rules, this is named tetraamminecopper(II) ion, where "tetraammine" indicates four ammonia ligands.

In summary, while \(H_2O\), \(CO\), and \(F^-\) have their IUPAC names correctly listed as aqua, carbonyl, and fluoro respectively, ammonia should be listed as "ammine" when it acts as a ligand in coordination complexes. This ensures consistency and clarity in chemical nomenclature.