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NCERT Exemplar · Class 9 Science Is Matter Around Us Pure

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Multiple Choice Questions 1–9 (part 1 of 4)

  1. Exercise 1

    Which of the following statements are true for pure substances?
    (i)
    Pure substances contain only one kind of particles
    (ii)
    Pure substances may be compounds or mixtures
    (iii)
    Pure substances have the same composition throughout
    (iv)
    Pure substances can be exemplified by all elements other than nickel
    (i)
    and (ii)
    (i)
    and (iii)
    (iii)
    and (iv)
    (ii)
    and (iii)

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    NCERT’s answer
    (b)
    (b) (i) and (iii) — a pure substance has one kind of particle and the same composition throughout; it is an element or compound, never a mixture, and nickel is no exception.

  2. Exercise 2

    Rusting of an article made up of iron is called
    (a)
    corrosion and it is a physical as well as chemical change
    (b)
    dissolution and it is a physical change
    (c)
    corrosion and it is a chemical change
    (d)
    dissolution and it is a chemical change

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    NCERT’s answer
    (c)
    (c) Corrosion, and it is a chemical change — iron reacts with oxygen and moisture in air to form a new substance, hydrated iron(III) oxide, so the metal's identity changes.

  3. Exercise 3

    A mixture of sulphur and carbon disulphide is
    (a)
    heterogeneous and shows Tyndall effect
    (b)
    homogeneous and shows Tyndall effect
    (c)
    heterogeneous and does not show Tyndall effect
    (d)
    homogeneous and does not show Tyndall effect

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    NCERT’s answer
    (d)
    (d) Homogeneous, and it does not show the Tyndall effect — sulphur dissolves in \(\displaystyle \text{CS}_2\) to give a true solution whose particles are too small to scatter light.

  4. Exercise 4

    Tincture of iodine has antiseptic properties. This solution is made by
    dissolving
    (a)
    iodine in potassium iodide
    (b)
    iodine in vaseline
    (c)
    iodine in water
    (d)
    iodine in alcohol

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    NCERT’s answer
    (d)
    (d) Iodine in alcohol — tincture of iodine is a solution of iodine dissolved in ethanol, applied on wounds and cuts for its antiseptic action.

  5. Exercise 5

    Which of the following are homogeneous in nature?
    (i)
    ice
    (ii)
    wood
    (iii)
    soil
    (iv)
    air
    (i)
    and (iii)
    (ii)
    and (iv)
    (i)
    and (iv)
    (iii)
    and (iv)

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    NCERT’s answer
    (c)
    (c) (i) and (iv) — ice is a pure substance and air a homogeneous mixture of gases, both uniform throughout; wood and soil are heterogeneous, with visibly different components.

  6. Exercise 6

    Which of the following are physical changes?
    (i)
    Melting of iron metal
    (ii)
    Rusting of iron
    (iii)
    Bending of an iron rod
    (iv)
    Drawing a wire of iron metal
    (i)
    , (ii) and (iii)
    (i)
    , (ii) and (iv)
    (i)
    , (iii) and (iv)
    (ii)
    , (iii) and (iv)

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    NCERT’s answer
    (c)
    (c) (i), (iii) and (iv) — melting, bending and wire-drawing only change iron's state or shape, with no new substance formed; rusting forms iron oxide, a chemical change.

  7. Exercise 7

    Which of the following are chemical changes?
    (i)
    Decaying of wood
    (ii)
    Burning of wood
    (iii)
    Sawing of wood
    (iv)
    Hammering of a nail into a piece of wood
    (i)
    and (ii)
    (ii)
    and (iii)
    (iii)
    and (iv)
    (i)
    and (iv)

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    NCERT’s answer
    (a)
    (a) (i) and (ii) — decaying and burning of wood form new substances (humus-like residues, ash, \(\displaystyle \text{CO}_2\)); sawing and hammering only change its shape, not its composition.

  8. Exercise 8

    Two substances, A and B were made to react to form a third substance,
    A2\displaystyle A_{2}B according to the following reaction
    2\displaystyle 2 A + B → A2\displaystyle A_{2} B
    Which of the following statements concerning this reaction are incorrect?
    (i)
    The product A2\displaystyle A_{2}B shows the properties of substances A and B
    (ii)
    The product will always have a fixed composition
    (iii)
    The product so formed cannot be classified as a compound
    (iv)
    The product so formed is an element
    (i)
    , (ii) and (iii),
    (ii)
    , (iii) and (iv)
    (i)
    , (iii) and (iv)
    (ii)
    , (iii) and (iv)

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    NCERT’s answer
    (c)
    (c) (i), (iii) and (iv) — the product is a compound, not an element, and it loses the separate properties of A and B; only its fixed composition, (ii), is a true statement.

  9. Exercise 9

    Two chemical species X and Y combine together to form a product P which
    contains both X and Y
    X + Y → P
    X and Y cannot be broken down into simpler substances by simple chemical
    reactions. Which of the following concerning the species X, Y and P are correct?
    (i)
    P is a compound
    (ii)
    X and Y are compounds
    (iii)
    X and Y are elements
    IS MATTER AROUND US PURE
    (iv)
    P has a fixed composition
    (i)
    , (ii) and (iii),
    (i)
    , (ii) and (iv)
    (ii)
    , (iii) and (iv)
    (i)
    , (iii) and (iv)

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    NCERT’s answer
    (d)
    (d) (i), (iii) and (iv) — X and Y resist breakdown by simple reactions, so they are elements; their combination P is a compound with a fixed composition.