Which of the following pairs of atoms is unlikely to form a compound?

• A. Na and Cl
• B. H and O
• C. Ne and Ar
• D. C and O

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that atoms form compounds primarily by sharing or transferring electrons to achieve a stable electron configuration, often resembling the nearest noble gas configuration.
2. Step 2: Recognize that noble gases like Ne (Neon) and Ar (Argon) already have full valence electron shells, making them very stable and generally unreactive, so they rarely form compounds with each other or other elements.
3. Step 3: Analyze the other pairs: Na (Sodium) and Cl (Chlorine) form ionic compounds by electron transfer; H (Hydrogen) and O (Oxygen) form covalent compounds by sharing electrons; C (Carbon) and O (Oxygen) also form covalent compounds.
4. Step 4: Conclude that since Ne and Ar are both noble gases with full valence shells, they are unlikely to form compounds with each other or other elements under normal conditions.
5. Step 5: Therefore, the pair Ne and Ar is the correct answer because their full valence shells make compound formation highly unlikely.