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Practice each question, then open the answer or worked solution.
Pick the change that can be reversed from the following
Ans: The correct option is (b) melting of ghee. Ghee can be refrozen after it has melted. As a result, it's a reversible procedure (in winters it gets frozen on its own, even in the container).
Which of the following changes cannot be reversed?
Ans: The correct option is (a) Hardening of cement. Once cement is hardened, it cannot be changed into its original state. Therefore, it is an irreversible process.
An iron ring is heated. Which of the following statements about it is incorrect?
Ans: The right answer is (d), the ring changes its shape and the change cannot be reversed. When iron is heated, it expands, and when it cools, it shrinks back to its original size. As a result, iron melting is a reversible process.
While lighting a candle, Paheli observed the following changes
(i) Wax was melting
(ii) Candle was burning
(iii) Size of the candle was reducing
(iv) Melted wax was getting solidified
Of the above, the changes that can be reversed are
Ans: The correct option is (d) (i) and (iv) Wax was melting and Melted wax was getting solidified because it is a reversible process.
Salt can be separated from its solution (salt dissolved in water), because
Ans: The correct option is (d) Mixing of salt in water is a change that can be reversed by evaporation. The addition of salt to water is a reversible process.
Rolling of chapati and baking of chapati are the changes that
Ans: The correct option is (c) can be reversed and cannot be reversed, respectively. We can roll chapati into a ball of dough, however the chapatti cannot be uncooked once it has been cooked.
Iron rim is made slightly smaller than the wooden wheel. The rim is usually heated before fixing into the wooden wheel, because on heating the iron rim
Ans: The correct option is (d) Expands first, then on cooling contracts and fits onto the wooden wheel. Iron expands when heated. So when the smaller rim of iron is heated it will fit the size of the wooden wheel, and once it is cooled down, it will go back to the size to fit the wooden wheel tightly.