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Photo chemical reaction, The reaction which absorbs or releases light is called photochemical reaction, Eg: Photosynthesis, Water + Carbon dioxide + light > Glucose + Oxygen, 6H20 + 6CO2 + light > CeHi206 + 602, , *What could be the reason for storing certain medicines and chemicals in brown bottles?, , The materials present in them may get decomposed on exposure to sunlight and it, become useless.The brown colour act as a filter for light. That is certain medicines and, chemicals are storing in brown bottles.