When you added NaCl in water , you notice that when the water boils over,it causes the flame of the gas burner to turn bright orange. My question is,. how would you explaine the appearance of the color in the flame?.

Sodium glows with a red color when heated. Sodium vapor lamps, often used on highways, throw a bright yellow color. The yellow is from the sodium.

The standard qualitative test for sodium is to take a wire, dip it into a solution of an unknown, and put it into a bunsen burner flame. If you do this in qualitative analysis class, however, you'll almost surely find sodium. It's everywhere and it's easy to contaminate solutions with it in qual labs.