Prisha Garg
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Which of the following are chemical changes?

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NCERT Solutions for Class 9 Science Chapter 2
Is Matter Around Us Pure
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Exercises Questions
Page No-29
Questions No-11

Which of the following are chemical changes?

(a) Growth of a plant

(b) Rusting of iron

(c) Mixing of iron filings and sand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of a candle

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3 Answers

  1. 1. Chemical Changes:
    – Rusting of iron (b):
    – Involves a chemical reaction between iron, oxygen, and water, leading to the formation of iron oxide (rust).

    – Cooking of food (d):
    – Various chemical changes occur during cooking, including the Maillard browning reaction, caramelization, and denaturation of proteins.

    – Digestion of food (e):
    – A complex process where food undergoes chemical changes, breaking down into simpler substances with the help of digestive enzymes.

    – Burning of a candle (g):
    – Involves a chemical reaction between the wax and oxygen, producing carbon dioxide and water vapor.

    2. Physical Changes:
    – Growth of a plant (a):
    – Biological process, not involving a fundamental chemical change in the plant.

    – Mixing of iron filings and sand (c):
    – Physical change, as no new substances are formed.

    – Freezing of water (f):
    – A physical change where water changes its state from a liquid to a solid without altering its chemical composition.

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  2. Chemical changes are:
    (a) Growth of a plant

    (b) Rusting of iron

    (c) Cooking of food

    (d) Digestion of food

    (e) Burning of a candle

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  3. Following are Chemical changes.
    (a) Growth of a plant
    (b) Rusting of iron
    (c) Cooking of food
    (d) Digestion of food
    (e) Burning of a candle.

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