Electrolytes conduct via free-moving ions in molten or aqueous states.

Steps:

• Identify electrolytes: ionic compounds molten or dissolved in water produce free ions for conduction and electrolysis.
• Check aqueous sodium chloride: contains Na⁺ and Cl⁻ ions, so electrolysable (✓).
• Check copper(II) bromide: solid form lacks mobile ions, not electrolysable without specifying molten/aqueous (✗).
• Check graphite: covalent network solid conducts electronically, not ionically, so not electrolysable (✗).
• Check molten lead(II) bromide: molten state frees Pb²⁺ and Br⁻ ions, so electrolysable (✓).

Why B is correct:

• Matches electrolysis definition: only ionic substances with mobile ions (aqueous NaCl and molten PbBr₂) are marked ✓, per Faraday's laws of electrolysis.

Why the others are wrong:

• A: Identical to B, but question specifies B as correct row.
• C: Incorrectly marks aqueous NaCl as ✗, ignoring its free ions.
• D: Wrongly marks molten PbBr₂ as ✗ and aqueous NaCl as ✗, violating electrolyte criteria.

Final answer: B