Question

Compared with ionic compounds, molecular compounds


have lower melting points


are harder


have higher boiling points


are brittle

Answer 1

Only "have lower melting points" is correct.

Why: molecular (covalent) substances are held together in the solid state by relatively weak intermolecular forces (van der Waals, dipole–dipole, hydrogen bonding), so they generally melt and boil at much lower temperatures than ionic solids, which are held by strong electrostatic ionic bonds. Ionic solids are typically hard and brittle; molecular solids are usually softer (and often not brittle).