International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What is true about the ions in magnesium oxide compared to sodium chloride?

1. MgO only consists of monoatomic ions

2. MgO contains ions with a higher charge than in NaCl

3. NaCl has a more complex ionic structure than MgO

4. They are both gaseous at room temperature

The correct answer is: MgO contains ions with a higher charge than in NaCl

In magnesium oxide, the ions consist of magnesium ions (Mg²⁺) and oxide ions (O²⁻). This contrasts with sodium chloride, which contains sodium ions (Na⁺) and chloride ions (Cl⁻). The key difference lies in the charges of the ions involved. In magnesium oxide, the magnesium ion carries a charge of +2, while the oxide ion has a charge of -2. In sodium chloride, both the sodium and chloride ions have a charge of +1 and -1, respectively. This makes the charges in magnesium oxide higher in magnitude compared to those in sodium chloride, as magnesium oxide features ions with charges of ±2, making it characteristic of a compound with stronger ionic bonds owing to the greater attractive forces between the doubly charged ions. The presence of these higher charged ions in magnesium oxide contributes to its higher melting point and stronger lattice energy relative to sodium chloride. The other options do not accurately reflect the properties of these ionic compounds. For example, sodium chloride is not more complex in its ionic structure than magnesium oxide; both have relatively simple ionic lattices. Additionally, both compounds are solid at room temperature, rather than gaseous. Lastly, magnesium oxide does not consist solely of monoatomic