Electrical Conductivity in Solid and Molten States

Steps:

• Identify that conductivity requires mobile charge carriers like electrons or ions.
• Recall metals and alloys conduct via delocalized electrons in both solid and liquid forms.
• Note ionic substances like salts conduct only when molten due to ion mobility.
• Eliminate non-conductors like organics and many oxides.

Why A is correct:

• Alloys, being metallic mixtures, have delocalized electrons that enable conduction in solid (via lattice) and molten (via liquid metal flow) states, per metallic bonding theory.

Why the others are wrong:

• B: Hydrocarbons are covalent non-polar molecules with no free charges, acting as insulators in all states.
• C: Metal oxides are typically ionic or ceramic insulators; they don't conduct well solid or molten without doping.
• D: Salts conduct only when molten (ions mobile) but not solid (ions fixed in lattice).

Final answer: A