Metals conduct heat and have high melting points due to metallic bonding

Steps:

• Recall that metals have delocalized electrons, allowing conduction of heat and electricity in solid form.
• Identify properties: high melting points from strong metallic bonds; malleable, not brittle.
• Eliminate non-metals: low melting points and brittleness indicate covalent or ionic structures.
• Match options to metallic traits: conduction when solid points to metals.

Why D is correct:

• High melting point and heat conduction when solid match metallic bonding, where electrons carry heat efficiently.

Why the others are wrong:

• A describes ionic compounds, which conduct only when molten or dissolved due to free ions.
• B describes non-metals or molecular solids, with weak forces causing low melting points and brittleness.
• C describes giant covalent structures like diamond, which have high melting points but do not conduct heat well.

Final answer: D