Which gas is known to conduct electric current?

Neon is known to conduct electric current, particularly when used in gas discharge tubes. In these tubes, when an electric current passes through the neon gas, it becomes ionized. This ionization enables the conduction of electricity and produces a bright light, which is why neon is commonly used in signs and decorative lighting. The ability of certain noble gases, like neon, to conduct electricity under specific conditions is linked to their atomic structure, where they have a complete outer electron shell, allowing them to be stable yet capable of electrical excitation at higher energies.

In contrast, hydrogen does not conduct electricity in its gaseous state, as its diatomic molecules do not allow free electrons for conduction. Cyclopropane, being an organic compound, does not conduct electricity as it is a hydrocarbon that lacks free ions. Nitrogen is similar to hydrogen in that it is a diatomic and non-metal gas with no free electrons to facilitate current flow. Thus, among the given options, neon stands out as the gas capable of conducting electric current when ionized.