Hydronium ion is formed when a molecule of water combines with

Options

A. Hydrogen atom
B. Proton
C. Hydrogen molecule
D. Oxygen atom

Explanation

To solve the question "Hydronium ion is formed when a molecule of water combines with," we will analyze the options provided and determine which one leads to the formation of a hydronium ion (H₃O⁺).

### Step-by-Step Solution:

1. **Understanding the Hydronium Ion**:
- The hydronium ion (H₃O⁺) is formed when a water molecule (H₂O) combines with a proton (H⁺).
- A proton is essentially a hydrogen ion, which carries a positive charge.

2. **Analyzing the Options**:
- **Option 1: Hydrogen Atom (H)**:
- A hydrogen atom does not have a charge (it is neutral). Therefore, it cannot combine with water to form a hydronium ion.
- **Conclusion**: This option is incorrect.

- **Option 2: Proton (H⁺)**:
- A proton (H⁺) is positively charged. When it combines with a water molecule, the oxygen in water donates a lone pair of electrons to the proton, forming the hydronium ion (H₃O⁺).
- **Conclusion**: This option is correct.

- **Option 3: Hydrogen Molecule (H₂)**:
- A hydrogen molecule (H₂) is neutral and does not have a charge. Therefore, it cannot form a hydronium ion with water.
- **Conclusion**: This option is incorrect.

- **Option 4: Oxygen Atom (O)**:
- An oxygen atom does not have a positive charge and cannot combine with water to form a hydronium ion.
- **Conclusion**: This option is incorrect.

3. **Final Conclusion**:
- The only option that leads to the formation of a hydronium ion when combined with water is the proton (H⁺). Therefore, the correct answer is **Option 2: Proton (H⁺)**.