What is a chemical entity that forms a complex ion around a central atom?

A coordination complex consists of a central atom or Jon, which usually metallic and is called the coordination centre, and a surrounding array of bound molecules or ions, that are in turn known as ligand or complexing agents

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.

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