A coordination compound consists of a central metal ion or atom bonded to ligands, which are molecules or ions capable of donating electron pairs. Step 1: Evaluate the choices - Option 1: Although coordination compounds can possess a defined molecular formula, this is not their primary defining characteristic. - Option 2: Coordination compounds do not inherently exhibit high melting points or electrical conductivity in their solid form; these properties are more characteristic of ionic compounds. - Option 3: The defining feature of a coordination compound is the bond formed between a central metal atom/ion and its surrounding ligands. This option accurately describes the compound. - Option 4: Coordination compounds may exhibit solubility in water, particularly if they form ions when dissolved. Answer: The defining characteristic of a coordination compound is option (3), which states that it comprises a central metal atom/ion bound to multiple ligands.