NEET Chemistry Structure of Atom / परमाणु संरचना NEET PYQ-Structure of Atom

  • question_answer
    Magnetic moment 2.84 BM is given by (At. no. Ni = 28, Ti = 22, Cr = 24, Co = 27)                        [NEET 2015 ]

    A)  \[N{{i}^{2+}}\]                     

    B)       \[T{{i}^{3+}}\]

    C)  \[C{{r}^{3+}}\]                     

    D)  \[C{{O}^{2+}}\]

    Correct Answer: A

    Solution :

    Magnetic moment, \[\mu =\sqrt{n(n+2)}\,BM\] where,
    \[n=\]number of unpaired electrons
    \[\mu =2.84\,(given)\]
    \[\therefore \]      \[284=\sqrt{n(n+2)}B.M\]
                            \[{{(2.84)}^{2}}=n(n+2)\]
                            \[8={{n}^{2}}+2n\]
                            \[{{n}^{2}}+2n-8=0\]
                            \[{{n}^{2}}+4n-2n-8=0\]
                            \[n(n+4)-2(n+4)=0\]
                            \[n=2\]
    \[N{{i}^{2+}}=[Ar]3{{d}^{8}}4{{s}^{0}}\] (two unpaired electrons)
    \[T{{i}^{3+}}=[Ar]3{{d}^{1}}4{{s}^{0}}\] (one unpaired electrons)
    \[C{{r}^{3+}}=[Ar]3{{d}^{3}},\] (three unpaired electrons)
    \[C{{o}^{2+}}=[Ar],3{{d}^{7}},4{{s}^{0}}\] (three unpaired  electrons)
    So, only \[N{{i}^{2+}}\] has 2 unpaired electrons.


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