The correct answer is 4. Plants.
Plants use carbon dioxide for the photosynthesis process where they use carbon dioxide to form energy rich molecules and release oxygen to the atmosphere. The carbon is present in atmosphere as carbon dioxide in higher concentration and methane in lower concentration. Carbon dioxide is removed by several processes such as by the formation of carbonic acid when the surface ocean water cool down and absorb more carbon dioxide near the poles, through conversion of the reduced carbon to carbonates or organic tissues like shells and by photosynthesis of plants which is an exchange process where plants absorb carbon dioxide and in turn release oxygen.