The hybridization of the central atom will change when :

Options

A. `NH_(3)` combines with `H^(+)`
B. `H_(3)BO_(3)` combines with`OH^(-)`
C. `NH_(3)` forms `NH_(2)^(-)`
D. `H_(2)O` combines with `H^(+)`

Explanation

To determine when the hybridization of the central atom changes, we can follow these steps:

### Step 1: Understand Hybridization
Hybridization is the mixing of atomic orbitals to form new hybrid orbitals, which can accommodate the bonding pairs and lone pairs of electrons around a central atom. The type of hybridization depends on the steric number, which is the sum of the number of sigma bonds and lone pairs around the central atom.

### Step 2: Calculate the Steric Number
The steric number can be calculated using the formula:
\[ \text{Steric Number} = \text{Number of Sigma Bonds} + \text{Number of Lone Pairs} \]

### Step 3: Analyze Examples
1. **Ammonia (NH3)**:
- Nitrogen has 5 valence electrons.
- It forms 3 sigma bonds with hydrogen and has 1 lone pair.
- Steric number = 3 (bonds) + 1 (lone pair) = 4.
- Hybridization = sp³.

2. **Ammonium Ion (NH4⁺)**:
- Nitrogen still has 5 valence electrons.
- It forms 4 sigma bonds and has no lone pairs.
- Steric number = 4 (bonds) + 0 (lone pairs) = 4.
- Hybridization = sp³ (no change).

3. **Boric Acid (H3BO3)**:
- Boron has 3 valence electrons.
- It forms 3 sigma bonds with hydroxyl groups and has no lone pairs.
- Steric number = 3 (bonds) + 0 (lone pairs) = 3.
- Hybridization = sp².

4. **Change in Hybridization**:
- When boric acid (sp²) combines with OH⁻, it changes to sp³ due to the addition of another bond, increasing the steric number to 4.

### Step 4: Check Other Examples
- **Water (H2O)**:
- Oxygen has 6 valence electrons.
- It forms 2 sigma bonds and has 2 lone pairs.
- Steric number = 2 (bonds) + 2 (lone pairs) = 4.
- Hybridization = sp³.

- **Hydronium Ion (H3O⁺)**:
- Oxygen loses one electron, forming 3 sigma bonds and 1 lone pair.
- Steric number = 3 (bonds) + 1 (lone pair) = 4.
- Hybridization = sp³ (no change).

### Conclusion
The hybridization of the central atom changes when the steric number changes due to the addition or removal of bonds or lone pairs. In the case of boric acid, the hybridization changes from sp² to sp³ when it combines with OH⁻.

### Final Answer
The hybridization of the central atom will change when it forms new bonds that alter the steric number, such as in the case of boric acid (H3BO3) changing from sp² to sp³ upon reacting with hydroxide ions.

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