Ionic Compounds Have High Melting Points Due to Strong Electrostatic Forces

Steps:

• Identify magnesium oxide (MgO) as formed from magnesium and oxygen, resulting in Mg²⁺ and O²⁻ ions.
• Recognize MgO's structure as a giant ionic lattice with ions held by strong electrostatic attractions.
• Understand that melting requires breaking these attractions to separate ions, demanding high energy.
• Conclude high melting point from the strength and extent of ionic bonding in the lattice.

Why D is correct:

• Ionic compounds like MgO consist of a lattice of oppositely charged ions attracted by strong electrostatic forces, requiring significant energy to overcome for melting, as per Coulomb's law (F = k * q₁q₂/r²).

Why the others are wrong:

• A: Metallic bonds involve delocalized electrons in metals; MgO is ionic, not metallic.
• B: MgO lacks discrete molecules; forces are between ions in a lattice, not molecules.
• C: Simple molecular substances have weak intermolecular forces, leading to low melting points, unlike MgO's ionic structure.

Final answer: D