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.
The brown deposits are due to rusting, and this is a chemical change.
Folding a handkerchief is a physical change and can be reversed.
A chemical process in which a substance reacts with oxygen with evolution of heat is called combustion, and this is a chemical change.
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.
Explanation
(i) The chapter explains that rusting of iron forms a brown-coloured substance called rust (iron oxide), which is a chemical change. (ii) Folding only changes the shape of the handkerchief without forming any new substance, making it a physical change that can be reversed by unfolding. (iii) The chapter defines combustion as a chemical reaction in which a substance reacts with oxygen and produces heat and/or light. (iv) The chapter describes that burning magnesium produces magnesium oxide (a white powder) and this is a chemical change as a new substance is formed.