Fill in the blanks by choosing the appropriate word/words from those given in the brackets: (double salts, complex compounds, uni, bi, six, four, three, coordination, linkage, imperfect, perfect, normal, penetrating, central ion, chelating, Werner, Pauling)
A complex ion contains a metal atom or ion which is known as.......

Explanation

To solve the question, we need to fill in the blank with the appropriate term that describes the metal atom or ion in a complex ion.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the term used to describe the metal atom or ion in a complex ion.

2. **Identifying Key Terms**: In coordination chemistry, a complex ion consists of a central metal atom or ion surrounded by molecules or anions known as ligands.

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