Give reasons :a. Photosynthesis is a chemical change. b. Sublimation is a physical change. c. Evaporation is faster when heat is applied. d. An iron rod changes its colour when exposed to air and water for too long.
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The chemical reaction which takes place in photosynthesis process involves reaction between six mole of carbon dioxide and six mole of water to form one mole of glucose and six mole of oxygen. As a new product is formed in this process, therefore photosynthesis is a chemical change.
Sublimation is a physical change because it is just the change of a solid substance to it's vapour state ,no new substance is formed and it can be again converted to solid this means it is a reversible change.
When substances made of iron are exposed to oxygen and moisture (water), rusting takes place. Rusting removes a layer of material from the surface and makes the substance weak.
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