Metals conduct electricity due to delocalized electrons Steps:

• Identify key metal property: electrical conductivity in solid and molten states from free electrons.
• Eliminate options lacking solid-state conduction, as metals conduct without melting.
• Note metals usually have high melting points, but exceptions like mercury have low ones while still conducting.
• Select option matching conduction in both states.

Why D is correct:

• Describes a metal like mercury: low melting point but conducts electricity in solid and molten forms due to delocalized electrons.

Why the others are wrong:

• A: Matches ionic compounds (e.g., NaCl), which conduct only when molten as ions are free.
• B: Matches covalent network solids (e.g., diamond), insulators in all states due to localized electrons.
• C: Matches molecular covalent substances (e.g., iodine), poor conductors always due to no free charges.

Final answer: D