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NCERT Exemplar · Class 10 Science Periodic Classification of Elements

52 questions · 52 still being checked

Short Answer Questions 37–41 (part 5 of 6)

  1. Exercise 37

    Identify and name the metals out of the following elements whose electronic configurations are given below.
    (a)
    2\displaystyle 2, 8\displaystyle 8, 2\displaystyle 2
    (b)
    2\displaystyle 2, 8\displaystyle 8, 1\displaystyle 1
    (c)
    2\displaystyle 2, 8\displaystyle 8, 7\displaystyle 7
    (d)
    2\displaystyle 2, 1\displaystyle 1

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    NCERT’s answer
    (a), (b) and (d)
    (a)
    Magnesium
    (b)
    Sodium
    (d)
    Lithium
    (a)
    \(\displaystyle 2,8,2\): \(\displaystyle \mathrm{Mg}\), $\displaystyle 2$ valence \(\displaystyle e^-\) \(\displaystyle \Rightarrow\) lost easily \(\displaystyle \Rightarrow\) metal.
    (b)
    \(\displaystyle 2,8,1\): \(\displaystyle \mathrm{Na}\), $\displaystyle 1$ valence \(\displaystyle e^-\) \(\displaystyle \Rightarrow\) lost easily \(\displaystyle \Rightarrow\) metal.
    (c)
    \(\displaystyle 2,8,7\): \(\displaystyle \mathrm{Cl}\), $\displaystyle 7$ valence \(\displaystyle e^-\) \(\displaystyle \Rightarrow\) gains $\displaystyle 1$ \(\displaystyle e^-\) \(\displaystyle \Rightarrow\) non-metal.
    (d)
    \(\displaystyle 2,1\): \(\displaystyle \mathrm{Li}\), $\displaystyle 1$ valence \(\displaystyle e^-\) \(\displaystyle \Rightarrow\) lost easily \(\displaystyle \Rightarrow\) metal.
    Answer: metals are (a) \(\displaystyle \mathrm{Mg}\), (b) \(\displaystyle \mathrm{Na}\), (d) \(\displaystyle \mathrm{Li}\).

  2. Exercise 38

    Write the formula of the product formed when the element A (atomic number 19\displaystyle 19) combines with the element B (atomic number 17\displaystyle 17). Draw its electronic dot structure. What is the nature of the bond formed?

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    Hint— A B Ionic bond. \(\displaystyle \mathrm{A}=\mathrm{K}\) (Potassium) \(\displaystyle \mathrm{B}=\mathrm{Cl}\) (Chlorine) NCERT_Solution_Class10_Science_Exemplar_Ch5_Q38_ncert
    \(\displaystyle A\) (\(\displaystyle Z=19\)): \(\displaystyle 2,8,8,1\) \(\displaystyle \Rightarrow\) \(\displaystyle \mathrm{K}\), one loosely held valence electron. \(\displaystyle B\) (\(\displaystyle Z=17\)): \(\displaystyle 2,8,7\) \(\displaystyle \Rightarrow\) \(\displaystyle \mathrm{Cl}\), needs one electron to complete its octet. \[\mathrm{K} \rightarrow \mathrm{K^+} + e^- \] \[\mathrm{Cl} + e^- \rightarrow \mathrm{Cl^-} \] \[\mathrm{K^+} + \mathrm{Cl^-} \rightarrow \mathrm{KCl} \]Complete transfer of one electron, then electrostatic attraction between \(\displaystyle \mathrm{K^+}\) and \(\displaystyle \mathrm{Cl^-}\), makes the bond ionic (electrovalent). Answer: \(\displaystyle \mathrm{AB} = \mathrm{KCl}\); ionic (electrovalent) bond.

  3. Exercise 39

    Arrange the following elements in the increasing order of their metallic character Mg, Ca, K, Ge, Ga

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    Ge < Ga < Mg < Ca < K
    \(\displaystyle \mathrm{K, Ca, Ga, Ge}\) all sit in Period $\displaystyle 4$ (Groups $\displaystyle 1$, $\displaystyle 2$, $\displaystyle 13$, $\displaystyle 14$): nuclear charge rises across the row, so metallic character falls. \[\text{Period 4:}\quad \mathrm{K > Ca > Ga > Ge} \] \[\mathrm{Mg}\ (\text{Group 2}):\quad \mathrm{Ca > Mg}\ (\text{down the group}),\qquad \mathrm{Mg > Ga,\,Ge}\ (\text{Group 2 vs 13, 14}) \] Answer: \(\displaystyle \mathrm{Ge < Ga < Mg < Ca < K}\)

  4. Exercise 40

    Identify the elements with the following property and arrange them in increasing order of their reactivity
    (a)
    An element which is a soft and reactive metal
    (b)
    The metal which is an important constituent of limestone
    (c)
    The metal which exists in liquid state at room temperature

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    NCERT’s answer
    (a)
    Na or K
    (b)
    Ca
    (c)
    Hg
    Hg < Ca < Na < K
    (a)
    Soft, reactive metal cut with a knife: \(\displaystyle \mathrm{Na}\) (sodium).
    (b)
    Limestone is \(\displaystyle \mathrm{CaCO_3}\), so the metal is \(\displaystyle \mathrm{Ca}\) (calcium).
    (c)
    Liquid at room temperature: \(\displaystyle \mathrm{Hg}\) (mercury).
    Reactivity follows how readily each metal loses its valence electron(s):
    \[\mathrm{Hg}\ (\text{barely reacts}) < \mathrm{Ca}\ (\text{cold water}) < \mathrm{Na}\ (\text{vigorous}) \]
    Answer: (a) \(\displaystyle \mathrm{Na}\) (or \(\displaystyle \mathrm{K}\)) (b) \(\displaystyle \mathrm{Ca}\) (c) \(\displaystyle \mathrm{Hg}\); \(\displaystyle \mathrm{Hg < Ca < Na}\)

  5. Exercise 41

    Properties of the elements are given below. Where would you locate the following elements in the periodic table?
    (a)
    A soft metal stored under kerosene
    (b)
    An element with variable (more than one) valency stored under water.
    (c)
    An element which is tetravalent and forms the basis of organic chemistry
    (d)
    An element which is an inert gas with atomic number 2\displaystyle 2
    (e)
    An element whose thin oxide layer is used to make other elements corrosion resistant by the process of " anodising"

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    NCERT’s answer
    (a)
    Sodium (Na) Group $\displaystyle 1$ and Period $\displaystyle 3$ or Potassium (K) Group $\displaystyle 1$ and Period $\displaystyle 4$
    (b)
    Phosphorus (P) Group $\displaystyle 15$ and Period $\displaystyle 3$
    (c)
    Carbon (C) Group $\displaystyle 14$ and Period $\displaystyle 2$
    (d)
    Helium (He) Group $\displaystyle 18$ and Period $\displaystyle 1$
    (e)
    Aluminium (Al) Group $\displaystyle 13$ and Period $\displaystyle 3$
    (a)
    Soft metal kept under kerosene: \(\displaystyle \mathrm{Na}\), sodium, Group $\displaystyle 1$, Period 3.
    (b)
    Variable valency, stored under water: \(\displaystyle \mathrm{P}\), phosphorus (\(\displaystyle \mathrm{PCl_3}\), \(\displaystyle \mathrm{PCl_5}\)), Group $\displaystyle 15$, Period 3.
    (c)
    Tetravalent, basis of organic chemistry: \(\displaystyle \mathrm{C}\), carbon, Group $\displaystyle 14$, Period 2.
    (d)
    Inert gas, \(\displaystyle Z=2\): \(\displaystyle \mathrm{He}\), helium, Group $\displaystyle 18$, Period 1.
    (e)
    Thin oxide layer used in anodising: \(\displaystyle \mathrm{Al}\), aluminium (\(\displaystyle \mathrm{Al_2O_3}\)), Group $\displaystyle 13$, Period 3.
    Answer: (a) \(\displaystyle \mathrm{Na}\) (b) \(\displaystyle \mathrm{P}\) (c) \(\displaystyle \mathrm{C}\) (d) \(\displaystyle \mathrm{He}\) (e) \(\displaystyle \mathrm{Al}\)