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  1. It is light and strong. It can be hammered into sheets ( malleable) or pulled out into wires ( ductile ). It is a highly reactive metal, although it is corrosion resistant. A fresh film of aluminium is a good reflector of visible light and an excellent reflector of medium and far infrared radiation .

  2. Polyvinyl chloride, also called Polychloroethene or PVC, is a thermoplastic. It turns soft when heated and hard when cooled. Polyvinyl chloride is made by polymerization of the monomer vinyl chloride ( chloroethene) CH 2 =CHCl. PVC can be made softer and more flexible by adding plasticizers. Phthalates are often used to soften PVC in this way.

  3. DNA, short for deoxyribonucleic acid, is the molecule that contains the genetic code of organisms. This includes animals, plants, protists, archaea and bacteria. It is made up of two polynucleotide chains in a double helix. [1] DNA is in each cell in the organism and tells cells what proteins to make.

  4. Infobox references. Urea is an organic compound. It was first found in urine in 1773 by the French chemist Jean Rouelle. It is also called Carbamide, and its chemical names are Carbonyl Diamide (used in inorganic chemistry) and Diaminomethanal (used in organic chemistry ). In humans, it is a normal component of blood and many body tissues.