NEET Chemistry Classification of Elements and Periodicity in Properties / तत्त्वों का वर्गीकरण एवं गुणों में आवर्ति NEET PYQ-Classification Elements In Properties

  • question_answer
    Which of the following orders of ionic radii is correctly represented?                                        [AIPMT 2014]

    A)  \[{{H}^{-}}>,{{H}^{+}}>H\]

    B)       \[N{{a}^{+}}>{{F}^{-}}>{{O}^{2-}}\]

    C)  \[{{F}^{-}}>{{O}^{2-}}>N{{a}^{+}}\]

    D)       None of these

    Correct Answer: D

    Solution :

    (No option is correct)
    [a]  \[{{H}^{-}}>{{H}^{+}}>H\]
    It is known that radius of a cation is always smaller than that of a neutral atom due to decrease in the number of orbits.
    Whereas, the radius of anion is always greater than a cation due to decrease in effective nuclear charge. Hence, the correct order is      
    \[{{H}^{-}}>H>{{H}^{+}}\]
    [b] \[N{{a}^{+}}>{{F}^{-}}>{{O}^{2-}}\]
    The given species are isoelectronic as they contain same number of electrons. For isoelectronic species,
    \[ionic\text{ }radii\text{ }\propto \frac{1}{atomic\text{ }number}\]
    Ion: \[N{{a}^{+}}{{F}^{-}}{{O}^{2-}}\]
    Atomic number: 11 9 8
    Hence, the correct order of ionic radii is
    \[{{O}^{2-}}>{{F}^{-}}>N{{a}^{+}}\]
    [c] Similarly,    the   correct   option    is
    \[{{O}^{2-}}>{{F}^{-}}\,>N{{a}^{+}},\]
    [d] Ion               : \[A{{l}^{3+}}\]         \[M{{g}^{2+}}\]          \[{{N}^{3-}}\]
    Atomic number: 13         12         7
    Hence, the correct order is\[{{N}^{3-}}\,>M{{g}^{2+}}\,>A{{l}^{3+}}\].
     


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