Ionic compounds like potassium iodide have high melting points and conduct electricity only when molten

Steps:

• Identify potassium iodide (KI) as an ionic compound with strong bonds, leading to high melting point around 681°C.
• Note ionic solids do not conduct electricity due to fixed ions in lattice.
• Confirm molten ionic compounds conduct as mobile ions carry charge.
• Match options to high melting point, poor solid conductivity, good molten conductivity.

Why C is correct:

• Option C fits ionic compound definition: high melting point from lattice energy, conducts only when molten per mobile ion theory.

Why the others are wrong:

• A: Low melting point indicates simple molecular substance with weak forces.
• B: Good solid conductivity indicates metallic bonding with delocalized electrons.
• D: High melting point but no molten conductivity indicates covalent network solid like diamond.

Final answer: C