Which of the following oxides is ionic?

1. Analyze the question You are asked to pick the oxide that is ionic. The type of bonding in an oxide depends on the elements combined with oxygen.

2. Concept

• Metal + non-metal usually gives an ionic bond (electron transfer).
• Non-metal + non-metal gives a covalent bond (electron sharing).
• A big electronegativity difference (about 1.7 or more) points to ionic character.
• Metals on the left of the Periodic Table, especially Groups 1 and 2, form typical ionic oxides.

3. Step-by-step solution

• A. P₄O₁₀: phosphorus and oxygen are both non-metals, so the bonding is covalent. It is an acidic oxide.
• B. MgO: magnesium is a Group 2 metal and oxygen is a non-metal. Mg gives up 2 electrons to form Mg²⁺, and O gains them to form O²⁻. This is a typical ionic compound with a high melting point (about 2800°C). It is a basic oxide.
• C. Al₂O₃: aluminium is a metal, so it is largely ionic, but Al³⁺ is small and highly charged. It polarizes the oxide ion and gives the bond some covalent character. It is amphoteric, so it is not the "pure" ionic example.
• D. SO₂: sulphur and oxygen are both non-metals, so the bonding is covalent. It is a gas at room temperature.

4. Answer MgO is the clearest ionic oxide. Al₂O₃ is borderline (ionic with covalent character), and the exam wants the typical ionic one, which is MgO.

5. Tip Remember: Group 1 and 2 metal oxides are ionic and basic; non-metal oxides are covalent and acidic; Al₂O₃ and ZnO are amphoteric. When two options are metal oxides, choose the one from the most electropositive metal (here Mg, not Al).