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NCERT Exemplar · Class 10 Science Metals and Non-metals

65 questions · 65 still being checked

Multiple Choice Questions 21–30 (part 3 of 7)

  1. Exercise 21

    2\displaystyle 2 mL each of concentrated HCl, HNO3\displaystyle \mathrm{HNO}_3 and a mixture of concentrated HCl and concentrated HNO3\displaystyle \mathrm{HNO}_3 in the ratio of 3\displaystyle 3 : 1\displaystyle 1 were taken in test tubes labelled as A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C respectively. The metal could be
    (a)
    Al
    (b)
    Au
    (c)
    Cu
    (d)
    Pt

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    NCERT’s answer
    (b)
    (b) Au. \[\mathrm{HCl} : \mathrm{HNO_3} = 3 : 1 \quad (\text{aqua regia}) \] Au resists \(\displaystyle \mathrm{HCl}\) and \(\displaystyle \mathrm{HNO_3}\) separately but dissolves in aqua regia (tube C). Pt behaves the same way; Au is the metal usually cited.

  2. Exercise 22

    An alloy is
    (a)
    an element
    (b)
    a compound
    (c)
    a homogeneous mixture
    (d)
    a heterogeneous mixture

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    (c)
    (c) A homogeneous mixture. Melting and mixing two or more metals (or a metal and carbon) gives a solid solution with properties unlike the parent metals.

  3. Exercise 23

    An electrolytic cell consists of
    (i)
    positively charged cathode
    (ii)
    negatively charged anode
    (iii)
    positively charged anode
    (iv)
    negatively charged cathode
    (a) (i) and (ii)
    (b) (iii) and (iv)
    (c) (i) and (iii)
    (d)(ii)
    ad (iv)

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    NCERT’s answer
    (b)
    (b) (iii) and (iv). An external battery drives the cell: its negative terminal makes the cathode negative, its positive terminal makes the anode positive — opposite to a galvanic cell.

  4. Exercise 24

    During electrolytic refining of zinc, it gets
    (a)
    deposited on cathode
    (b)
    deposited on anode
    (c)
    deposited on cathode as well as anode
    (d)
    remains in the solution

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    NCERT’s answer
    (a)
    (a) Deposited on cathode. Cathode: \[\mathrm{Zn^{2+}} + 2e^- \rightarrow \mathrm{Zn} \] Anode: \[\mathrm{Zn} \rightarrow \mathrm{Zn^{2+}} + 2e^- \] Impure zinc anode dissolves in \(\displaystyle \mathrm{ZnSO_4}\) solution; pure zinc plates out on the cathode, insoluble impurities settle as anode mud.

  5. Exercise 25

    An element A is soft and can be cut with a knife. This is very reactive to air and cannot be kept open in air. It reacts vigorously with water. Identify the element from the following
    (a)
    Mg
    (b)
    Na
    (c)
    P (d) Ca

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    NCERT’s answer
    (b)
    (b) \(\displaystyle \mathrm{Na}\) — soft enough to cut with a knife, tarnishes instantly in air, and reacts vigorously with water, so it is stored under kerosene. \[2\mathrm{Na} + 2\mathrm{H_2O} \rightarrow 2\mathrm{NaOH} + \mathrm{H_2}\uparrow \]

  6. Exercise 26

    Alloys are homogeneous mixtures of a metal with a metal or non-metal. Which among the following alloys contain non-metal as one of its constituents?
    (a)
    Brass
    (b)
    Bronze
    (c)
    Amalgam
    (d)
    Steel

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    NCERT’s answer
    (d)
    (d) Steel — an alloy of iron with carbon, a non-metal; brass (Cu–Zn), bronze (Cu–Sn) and amalgam (metal–Hg) alloy metals only.

  7. Exercise 27

    Which among the following statements is incorrect for magnesium metal?
    (a)
    It burns in oxygen with a dazzling white flame
    (b)
    It reacts with cold water to form magnesium oxide and evolves hydrogen gas
    (c)
    It reacts with hot water to form magnesium hydroxide and evolves hydrogen gas
    (d)
    It reacts with steam to form magnesium hydroxide and evolves hydrogen gas

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    NCERT’s answer
    (b)
    (b) is incorrect — Mg does not react with cold water. Hot water gives the hydroxide; steam gives the oxide, so (d) is loosely worded, but (b) is the clear error. \[\mathrm{Mg} + 2\mathrm{H_2O}(\text{hot}) \rightarrow \mathrm{Mg(OH)_2} + \mathrm{H_2}\uparrow \] \[\mathrm{Mg} + \mathrm{H_2O}(\text{steam}) \rightarrow \mathrm{MgO} + \mathrm{H_2}\uparrow \]

  8. Exercise 28

    Which among the following alloys contain mercury as one of its constituents?
    (a)
    Stainless steel
    (b)
    Alnico
    (c)
    Solder
    (d)
    Zinc amalgam

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    NCERT’s answer
    (d)
    (d) Zinc amalgam — an amalgam is by definition an alloy of mercury with another metal, here zinc; the other three alloys contain no mercury.

  9. Exercise 29

    Reaction between X and Y, forms compound Z. X loses electron and Y gains electron. Which of the following properties is not shown by Z?
    (a)
    Has high melting point
    (b)
    Has low melting point
    (c)
    Conducts electricity in molten state
    (d)
    Occurs as solid

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    (b)
    (b) Has low melting point — \(\displaystyle X\) and \(\displaystyle Y\) form ionic \(\displaystyle Z\) by electron transfer: \[X \rightarrow X^{+} + e^{-}, \qquad Y + e^{-} \rightarrow Y^{-}, \qquad X^{+} + Y^{-} \rightarrow Z \] Strong electrostatic attraction gives \(\displaystyle Z\) a high melting point.

  10. Exercise 30

    The electronic configurations of three elements X, Y and Z are X — 2\displaystyle 2, 8\displaystyle 8; Y — 2\displaystyle 2, 8\displaystyle 8, 7\displaystyle 7 and Z — 2\displaystyle 2, 8\displaystyle 8, 2. Which of the following is correct?
    (a)
    X is a metal
    (b)
    Y is a metal
    (c)
    Z is a non-metal
    (d)
    Y is a non-metal and Z is a metal

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    (d)
    (d) \(\displaystyle Y:2,8,7\) needs one more electron for an octet — a non-metal; \(\displaystyle Z:2,8,2\) readily loses two electrons — a metal. \(\displaystyle X:2,8\) is a stable noble-gas configuration, not a metal.