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Fill in the blanks in the following statements:
(i) Nalini observed that the handle of her cycle has got brown deposits. The brown deposits are due to ________, and this is a ________ change.
(ii) Folding a handkerchief is a ________ change and can be ________.
(iii) A chemical process in which a substance reacts with oxygen with evolution of heat is called ________, and this is a ________ change.
(iv) Magnesium, when burnt in air, produces a substance called ________. The substance formed is ________ in nature. Burning of magnesium is a ________ change.
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(i) Nalini observed that the handle of her cycle has got brown deposits. The brown deposits are due to rusting , and this is a chemical change.
(ii) Folding a handkerchief is a physical change and can be reversed .
(iii) A chemical process in which a substance reacts with oxygen with evolution of heat is called combustion , and this is a chemical change.
(iv) Magnesium, when burnt in air, produces a substance called magnesium oxide . The substance formed is basic in nature. Burning of magnesium is a chemical change.
(Recall from "The World of Metals and Non-metals": metal oxides are usually basic; non-metal oxides are usually acidic. Magnesium is a metal, so its oxide is basic.)
