Which of the following ligands is NOT paired with the name it takes as a ligand in the IUPAC name of a complex?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → NH3, ammonia
In an IUPAC name a neutral ligand keeps its own name, with four special exceptions: aqua for \( \ce{H2O} \), ammine for \( \ce{NH3} \), carbonyl for CO and nitrosyl for NO. Anionic ligands take names ending in –o, in the –ido form (chlorido, cyanido, hydroxido).
Option (1) H2O, aqua — Correctly paired. Water as a ligand is named aqua.
Option (2) NH3, ammonia — Not correctly paired. Ammonia as a ligand is named ammine, as in hexaamminecobalt(III), not “ammonia”.
Option (3) CO, carbonyl — Correctly paired. Carbon monoxide as a ligand is named carbonyl, as in tetracarbonylnickel(0).
Option (4) F−, fluorido — Correctly paired. \( \ce{F^-} \) is an anionic ligand, so its name ends in –o in the –ido form, like chlorido for \( \ce{Cl^-} \).
NCERT (2026-27 edition):
5.3.2 Naming of Mononuclear Coordination Compounds – “(iii) Names of the anionic ligands end in –o, those of neutral and cationic ligands are the same except aqua for H2O, ammine for NH3, carbonyl for CO and nitrosyl for NO.”