NEET Chemistry Chemical Bonding and Molecular Structure / रासायनिक आबंधन एवं आणविक संरचना NEET PYQ-Chemical Bonding Molecular

  • question_answer
    Which   of   the   following   is paramagnetic?                                                                     [NEET 2013]

    A)  \[CO\]            

    B)       \[O_{2}^{-}\]             

    C)  \[C{{N}^{-}}\]                       

    D)       \[N{{O}^{+}}\]

    Correct Answer: B

    Solution :

    Paramagnetic species contains unpaired electrons in their molecular orbital electronic configuration.
    Molecular orbital configuration of the given species is as \[CO(6+8=14)=\sigma 1{{s}^{2}},\overset{*}{\mathop{\sigma }}\,1{{s}^{2}},\]\[\sigma 2{{s}^{2}},\overset{*}{\mathop{\sigma }}\,2{{s}^{2}},\pi 2p_{x}^{2}\approx \overset{*}{\mathop{\pi }}\,2p_{y}^{1}\]
    (All the electrons are paired so it is diamagnetic.) \[O_{2}^{-}(8+8+1=17)\]
    \[=\sigma 1{{s}^{2}},\overset{*}{\mathop{\sigma }}\,1{{s}^{2}},\overset{{}}{\mathop{\sigma }}\,2{{s}^{2}},\overset{*}{\mathop{\sigma }}\,{{s}^{2}},\overset{{}}{\mathop{\sigma 2p_{z}^{2}\pi 2p_{x}^{2}}}\,\]
    \[\overset{{}}{\mathop{\pi }}\,2p_{y}^{2},\overset{*}{\mathop{\pi }}\,2p_{x}^{2}\approx \overset{*}{\mathop{\pi }}\,2p_{y}^{1}\]
    It contains one unpaired electron so it is paramagnetic.
    \[C{{N}^{-}}(6+7+1=14)=\]same as CO
    \[N{{O}^{+}}(7+8-1)=\]same as CO
    Thus, among the given species only \[O_{2}^{-}\]is paramagnetic.


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