A COORDINATION COMPOUND consists of a central metal atom (or ion) BONDED to a set of surrounding molecules or ions, called

1. NCERT §5.1 (Werner's theory) introduces the vocabulary of coordination chemistry. 2. A coordination compound has a CENTRAL metal atom or ion (typically a transition metal) bonded to a definite number of ANCILLARY species via dative (coordinate covalent) bonds. 3. The ancillary species are called LIGANDS — neutral molecules (NH$_3$, H$_2$O, CO) or anions (Cl$^-$, OH$^-$, CN$^-$) that donate a lone pair to the metal. 4. Other options are unrelated: isotopes (B) refer to nuclear identity; buffer pairs (C) to pH chemistry; co-monomers (D) to polymerisation. _Source: NCERT Class 12 Chemistry Part 1, Ch 5 "Coordination Compounds", §5.1 (Werner's Theory and basic terms), p. 1–2._