Final answer:
The sodium ion creates an intense yellow flame when subjected to heat, due to the emission of light when electrons in the sodium atom return to their original energy state after being excited. This emission spectrum characteristic is utilized in various applications, including street lighting and the identification of sodium in qualitative analyses.
Step-by-step explanation:
The cation that has an intense yellow flame when introduced to a heat source is the sodium ion. This bright yellow color is the result of certain electrons in the sodium atom absorbing energy and jumping to a higher energy state. When the electrons return to their original energy state, they release energy in the form of light, which for sodium is predominately in the yellow part of the spectrum. This is an example of an emission spectrum and is a characteristic of sodium and its compounds.
Such a distinct coloration is often used for identification purposes in qualitative analysis during flame tests. In fact, industries including those that manufacture certain dyes, drugs, and perfumes utilize the unique light-emitting properties of sodium. Moreover, sodium vapor lights are widely used for street lighting because they penetrate fog effectively, which is attributed to the fact that fog does not scatter yellow light as much as white light.