Explanation:

Introduction:
The yellow color imparted to the Bunsen flame by sodium chloride can be explained by the emission of excess energy absorbed as radiation in the visible region. This phenomenon is known as flame coloration and is widely used in flame tests to identify the presence of certain elements.

Ionization Energy of Sodium:
The ionization energy of sodium refers to the energy required to remove an electron from a sodium atom in its gaseous state. While it is true that sodium has a relatively low ionization energy, this factor alone does not explain the yellow color observed in the Bunsen flame. The ionization energy determines the ease with which an atom loses an electron, but it does not directly relate to the emission of visible light.

Sublimation of Metallic Sodium:
Metallic sodium can indeed sublime, or transition from a solid to a vapor phase, at high temperatures. However, the yellow color observed in the Bunsen flame is not caused by the sublimation of metallic sodium to give yellow vapor. In a flame test, the compound being tested is introduced into the flame, and the observed color is due to the emission of light by the atoms or ions present in the compound, not the vaporization of the compound itself.

Emission of Excess Energy:
The correct explanation for the yellow color observed in the Bunsen flame is the emission of excess energy absorbed as radiation in the visible region. When sodium chloride is introduced into the flame, the heat of the flame causes the compound to dissociate into sodium and chloride ions. The high temperature of the flame excites the electrons in the sodium ions to higher energy levels. When these excited electrons return to their ground state, they release excess energy in the form of light. This released energy corresponds to a specific wavelength in the visible region, which appears as a yellow color.

Conclusion:
In conclusion, the yellow color imparted to the Bunsen flame by sodium chloride is due to the emission of excess energy absorbed as radiation in the visible region. This phenomenon occurs when the compound dissociates into sodium and chloride ions in the high-temperature flame, and the excited electrons in the sodium ions release energy in the form of yellow light when they return to their ground state.