The answer is chlorine
That is chlorine is the green-yellowish gas that is used as a disinfecting agent.
Among the options, iodine is a solid ,bromine is liquid while fluorine and chlorine are gases.
Chlorine is greenish yellow colored gas while fluorine is pale yellow, chlorine is used as a disinfecting agent and oxidizing agent as well.
I would say the answer is photosynthesis
Hope this helps
-Zayn Malik
