An ambidentate ligand is one which

Options

A. is linkage to the metal atom at two points
B. has two donor atoms but only one of them has the capacity to form a coordinate bond
C. has two donor atoms but either of the two can form a co-ordinate bond
D. forms chelate rings

Explanation

**Step-by-Step Solution:**

1. **Understanding Ambidentate Ligands**: An ambidentate ligand is a type of ligand that has two different donor atoms, but it can bind to the metal center through only one of those atoms at a time. This means that while the ligand has multiple potential binding sites, it does not bind through both simultaneously.

2. **Analyzing the Options**:
- **Option 1**: "Links to the metal at two points." This is incorrect because an ambidentate ligand does not bind at two points simultaneously; it binds at one point at a time.
- **Option 2**: "Has two donor atoms, but only one of them has the capacity to form a coordinate bond." This is also incorrect because both donor atoms can form coordinate bonds, but only one can do so at a time.
- **Option 3**: "Has two donor atoms, either of which can form a coordinate bond." This is correct. An ambidentate ligand has two donor atoms, and it can bind through either one, but not both at the same time.
- **Option 4**: "Forms chelate rings." This is incorrect because chelate formation typically involves bidentate or polydentate ligands that can bind through multiple sites simultaneously, forming ring structures.

3. **Conclusion**: The correct definition of an ambidentate ligand is given in **Option 3**: "Has two donor atoms, either of which can form a coordinate bond."

**Final Answer**: An ambidentate ligand is one that has two donor atoms, either of which can form a coordinate bond.

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