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)
Complexes such as `K_4[Fe(CN)_6]` in which the complex ion is quite stable and almost undissociated in solution are called ............. or .......... complexes.

Explanation

To solve the question, we need to fill in the blanks with the appropriate words from the options given in the brackets. The question refers to complexes like \( K_4[Fe(CN)_6] \), which is known as potassium ferrocyanide.

1. **Understanding the Nature of the Complex**:
- The complex ion \( [Fe(CN)_6]^{4-} \) is stable and does not dissociate significantly when dissolved in solution. This means it retains its structure and does not break down into its constituent ions easily.

2. **Identifying the Type of Complex**:
- Complexes that are stable and remain undissociated in solution are typically referred to as "perfect complexes" or "penetrating complexes". The term "perfect" indicates that the complex does not dissociate at all in solution, while "penetrating" suggests that it can enter the solution without breaking apart.

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