(4) Calcium Explanation: Chlorophyll, a photo-receptive pigment, allows plants to absorb sunlight and synthesize it into carbohydrates and oxygen. The basic formula for photosynthesis takes 6 molecules of carbon dioxide and 6 molecules of water, reacts them in the presence of chlorophyll and sunlight (a catalyst), and converts them into 1 molecule' of glucose and 6 molecules of oxygen. Chlorophyll is a chlorine pigment, which is structurally similar to and produced through the same metabolic pathway as other porphyrin pigments such as home.