Which one of the following contains a co-ordinate covalent bond?

Options

A. `H_(2)O`
B. `HCl`
C. `BaCl_(2)`
D. `overset(+)N_(2)H_(5)`

Explanation

To determine which of the given options contains a coordinate covalent bond, we need to analyze each option carefully. A coordinate covalent bond is formed when one atom donates a pair of electrons to another atom that does not have a complete octet.

### Step-by-Step Solution:

1. **Understanding Coordinate Covalent Bonds**:
- A coordinate covalent bond occurs when one atom provides both electrons for a shared pair. This typically happens when one atom has a lone pair of electrons and another atom has an empty orbital.

2. **Analyzing Each Option**:
- **Option 1: Water (H₂O)**:
- In water, oxygen has 6 valence electrons and shares one electron with each hydrogen atom. This results in the formation of two covalent bonds, but no coordinate bond is present since both atoms contribute electrons.

- **Option 2: Hydrogen Chloride (HCl)**:
- In HCl, chlorine has 7 valence electrons and shares one electron with hydrogen. This forms a covalent bond, but again, there is no coordinate bond as both atoms are contributing electrons.

- **Option 3: Barium Chloride (BaCl₂)**:
- In BaCl₂, barium donates its two electrons to two chlorine atoms. This is an ionic bond formation and does not involve coordinate covalent bonding.

- **Option 4: Hydrazinium ion (N₂H₅⁺)**:
- In N₂H₅⁺, nitrogen atoms can have lone pairs. When a hydrogen ion (H⁺) approaches, one of the nitrogen atoms can donate its lone pair to bond with the H⁺ ion, forming a coordinate covalent bond.

3. **Conclusion**:
- Among the options analyzed, **Option 4 (N₂H₅⁺)** is the only one that contains a coordinate covalent bond.

### Final Answer:
The option that contains a coordinate covalent bond is **N₂H₅⁺**.

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