Polyethylene (polythene) softens on heating and hardens on cooling, so it is thermoplastic. Bakelite is thermosetting; rubber is elastomer; silk is natural polymer.
Explanation:
Haematite (Fe₂O₃) is a major ore of iron. Bauxite is aluminium ore, galena is lead sulfide, cinnabar is mercury sulfide. Magnetite (Fe₃O₄) is another iron ore.
Explanation:
The strong nuclear force is the attractive force that binds protons and neutrons (nucleons) together in the nucleus, overcoming the electrostatic repulsion between protons. It is short-range and charge-independent. Electrostatic repulsion would otherwise blow the nucleus apart. Gravitational force is negligible at this scale. Van der Waals forces operate between molecules.
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