The correct answer is option 4: Neon. When electricity flows through neon gas, it produces a red light.

To understand why this happens, we need to consider the concept of gas discharge lamps. These are lamps filled with a specific gas or a mixture of gases. When an electric current passes through the gas, it excites the atoms or molecules in the gas. As these excited particles return to their ground state, they release energy in the form of light.

In the case of neon gas, the excitation and de-excitation processes result in the emission of red light. This is because the energy levels of the electrons in neon atoms are such that when they gain energy from the electric current and then release it, they emit light at a specific wavelength that corresponds to the red color.

It`s important to note that each gas emits light at different wavelengths depending on the energy levels of its atoms or molecules. For example, helium (option 1) produces a pinkish-orange light, argon (option 2) emits a bluish-purple light, and nitrogen (option 3) emits a variety of colors depending on the specific conditions.

Therefore, when electricity flows through neon gas, it emits a red light.