Which of the following substances conducts electricity?

- (1) Diamond: Diamond does not conduct electricity. It is an insulator because it has no free electrons or ions to carry charge. The carbon atoms in diamond form a strong covalent network, preventing the free flow of electrons.
- (2) Sulphur (solid): Sulphur in its solid form also does not conduct electricity. It is a non-metal and does not have free electrons or charged particles to facilitate conduction.
- (3) Molten \(\mathrm{NaCl}:\) Molten NaCl (sodium chloride in its liquid form) conducts electricity. When NaCl is heated to its melting point, it dissociates into free sodium ( \(\mathrm{Na}^{+}\)) and chloride ions \(\left(\mathrm{Cl}^{-}\right)\), which are able to move freely and carry an electric current.
- (4) Crystalline NaCl: Crystalline NaCl (solid sodium chloride) does not conduct electricity. While it contains ions ( \(\mathrm{Na}^{+}\)and \(\mathrm{Cl}^{-}\)), they are not free to move in the solid state. For conduction, the ions need to be a mobile, which happens only in the molten state