Which cation is responsible for producing an orange flame color?

The cation that produces an orange flame color is sodium (Na⁺). When sodium salts are heated, they emit a bright yellow-orange flame due to the excitation of sodium atoms. This occurs because when the atoms are heated, the electrons gain energy and move to a higher energy level. When they return to their ground state, they release this energy in the form of light. For sodium, this light falls within the spectrum that we perceive as an orange-yellow color.

The other cations listed have different flame colors when introduced to a flame. For instance, lithium produces a crimson flame, potassium gives off a lilac flame, and magnesium does not produce a characteristic flame color in the same way that alkali metals do. Therefore, sodium is distinctly recognized for its signature orange flame, making it the correct answer.