BCECE Engineering BCECE Engineering Solved Paper-2002

  • question_answer
    Coordination number and oxidation number of Cr in \[{{K}_{3}}Cr{{({{C}_{2}}{{O}_{4}})}_{3}}\]are respectively:

    A) 6 and \[+\,3\]     

    B)        4 and\[-\,2\]

    C) 3 and 0                 

    D)        3 and\[+\,3\]

    Correct Answer: A

    Solution :

    Key Idea: (i) Coordination of central atom is number of lone pair of electrons donated by ligands (ii) The sum of oxidation number of all elements in coordination compound is always zero. \[{{K}_{3}}[Cr{{({{C}_{2}}{{O}_{4}})}_{3}}]\] \[\because \]Oxalate is bidentate ligand so coordination number of \[\text{Cr}\,\text{=}\,\text{6}\] Let oxidation number of Cr in                                 \[{{K}_{3}}[Cr{{({{C}_{2}}{{O}_{4}})}_{3}}]=x\]                 or            \[(+\,1\,\times \,3)+x+(-2\times 3)=0\]                 or            \[3+x-6=0\]                 \[\therefore \]  \[x=+\,3\] \[\therefore \]Coordination number of Cr in given compound is 6 and oxidation number + 3


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