Which pair of atoms form strongest ionic bond ?

Options

A. Al and As
B. Al and N
C. Al and Se
D. Al and O

Explanation

To determine which pair of atoms forms the strongest ionic bond, we need to analyze the properties of the involved elements, specifically focusing on their ionization enthalpy and electron affinity.

### Step-by-Step Solution:

1. **Identify the Elements**: The question provides a metal (aluminum) and four non-metals (arsenic, selenium, nitrogen, and oxygen). We need to evaluate the electron affinity of these non-metals.

2. **Understand Ionic Bond Formation**: Ionic bonds form between metals and non-metals. The strength of the ionic bond depends on:
- The **ionization enthalpy** of the metal (which should be low).
- The **electron affinity** of the non-metal (which should be high).

3. **Evaluate Electron Affinity**: Among the non-metals listed:
- **Oxygen** has the highest electron affinity.
- **Nitrogen** has a lower electron affinity compared to oxygen.
- **Selenium** and **arsenic** have even lower electron affinities than nitrogen.

4. **Conclusion on Bond Strength**: Since aluminum has a low ionization enthalpy and oxygen has the highest electron affinity among the given non-metals, the pair of aluminum and oxygen will form the strongest ionic bond.

5. **Final Answer**: Therefore, the pair of atoms that form the strongest ionic bond is **Aluminum (Al) and Oxygen (O)**.