Plastics are made by the process of polymerisation, Plastics are classified as either thermoplastics or thermosetting plastics., Plastics are hazardous to the environment because many are nonbiodegradable, Metals are useful because they are lustrous and strong, An alloy is a mixture of two or more metals, metal + oxygen = metal oxide, metal + water = metal hydroxide + hydrogen, metal + acid = salt + hydrogen, metal + alkali = alkali salt + hydrogen., Aluminium on exposure to air produces a protective oxide coat, Corrosion forms metal oxides, The type of corrosion depends on the environmental conditions, Most metals corrode in moist air. , Metals become tarnished when a layer of metal oxide is formed on the surface, The corroded product of iron is called rust..




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