Coordinate linkage is formed

Options

A. By transfer of one electron from one atom to another
B. By the loss of one electron each from both the atoms
C. By sharing of one electron from each atom
D. When contribution of one electron pair is made by one atom and both the atoms share equally

Answer

### Step-by-Step Solution:

1. **Understanding Coordinate Linkage**:
- A coordinate bond, also known as a dative bond, is a type of covalent bond where both electrons in the bond come from the same atom.

2. **Definition of Coordinate Bond**:
- In a coordinate bond, one atom donates a pair of electrons to another atom that has an empty orbital, allowing both atoms to share the electrons.

3. **Examples of Coordinate Bond**:
- A common example of a coordinate bond is the formation of the ammonium ion (NH₄⁺) from ammonia (NH₃) and a hydrogen ion (H⁺). In this case, nitrogen donates a lone pair of electrons to the hydrogen ion.

4. **Analyzing the Options**:
- **Option 1**: Transfer of one electron from one atom to another - This describes an ionic bond, not a coordinate bond.
- **Option 2**: Loss of one electron each from both atoms - This does not describe a coordinate bond.
- **Option 3**: Sharing of electron from each atom - This describes a typical covalent bond, not a coordinate bond.
- **Option 4**: Contribution of one electron pair made by one atom and both atoms share equally - This accurately describes a coordinate bond.

5. **Conclusion**:
- Based on the definitions and examples provided, the correct answer to the question "Coordinate linkage is formed by" is **Option 4**.