What is the color of chlorine? 

Green yellow

The correct answer is option 3. Green yellow.

Chlorine gas (Cl₂) has a distinctive yellow-green color. This color is a result of the absorption of light in the red region of the electromagnetic spectrum by chlorine molecules. When chlorine gas is exposed to light, it absorbs energy in the red part of the spectrum, leaving the transmitted light with a greenish-yellow appearance.

The color of chlorine is a helpful visual indicator, and it's one of the characteristics that aid in identifying its presence. This yellow-green color is particularly noticeable when chlorine is in its gaseous form. Keep in mind that the color may not be as prominent when chlorine is dissolved in water or involved in chemical reactions where its gaseous form is not present.