Introduction:
When certain elements are introduced into a Bunsen flame, they can impart characteristic colors to the flame. This phenomenon is known as flame coloration and is often used in qualitative analysis to identify the presence of specific elements or compounds. In the case of alkaline earth metals, they can produce distinct flame colors when their chlorides are introduced into a Bunsen flame.

Explanation:
1. Flame Coloration:
Flame coloration occurs due to the excitation of electrons in the atoms or ions of the elements present in the flame. When energy is applied to the system, electrons in the ground state are promoted to higher energy levels. As these excited electrons return to their ground state, they release energy in the form of light, resulting in the characteristic flame color.

2. Alkaline Earth Metals:
Alkaline earth metals belong to Group 2 of the periodic table and include elements such as beryllium, magnesium, calcium, strontium, barium, and radium. These metals have two valence electrons, which are relatively easy to remove, leading to their high reactivity. When the chlorides of alkaline earth metals are introduced into a Bunsen flame, they exhibit distinct flame colors due to the excitation of their electrons.

3. Flame Colors of Alkaline Earth Metals:
Each alkaline earth metal produces a characteristic flame color when its chloride is introduced into a Bunsen flame. The flame colors of some of the alkaline earth metals are as follows:

- Beryllium: No characteristic flame color
- Magnesium: Pale white flame
- Calcium: Brick red flame
- Strontium: Crimson red flame
- Barium: Green flame
- Radium: Not commonly observed in laboratory settings

4. Reason for Barium Imparting Green Color:
Barium, specifically its chloride compound, imparts a green color to the Bunsen flame. This green color is due to the excitation of the barium atoms or ions in the flame. As the electrons in the barium atoms or ions are excited and then return to their ground state, they release energy in the green portion of the electromagnetic spectrum, resulting in the observed green flame color.

Conclusion:
In the case of alkaline earth metals, barium imparts a green color to the Bunsen flame when introduced in the form of its chloride. This characteristic flame color is useful in qualitative analysis to identify the presence of barium in a sample.