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 bridging ligand must contain atleast......electron pairs for coordination.

Explanation

To solve the question, we need to determine how many electron pairs a bridging ligand must contain for coordination.

### Step-by-Step Solution:

1. **Understanding Bridging Ligands**: A bridging ligand is a type of ligand that connects two or more metal ions in a coordination complex.

2. **Electron Pairs Requirement**: For a ligand to effectively bridge between two metal ions, it must be able to donate electron pairs to both metal centers.

...