BCECE Engineering BCECE Engineering Solved Paper-2004

  • question_answer
    Which of the following has least oxidation state of Fe?

    A) \[{{K}_{3}}[Fe{{(OH)}_{6}}]\]

    B)        \[{{K}_{2}}[Fe{{O}_{4}}]\]

    C) \[FeS{{O}_{4}}{{(N{{H}_{4}})}_{2}}S{{O}_{4}}.6{{H}_{2}}O\]

    D) \[{{[Fe{{(CN)}_{6}}]}^{3-}}\]

    Correct Answer: C

    Solution :

    Key Idea: Find oxidation state of Fe in all compound to find which has Fe in least oxidation state \[{{\text{K}}_{\text{3}}}\text{ }\!\![\!\!\text{ Fe(OH}{{\text{)}}_{\text{6}}}\text{ }\!\!]\!\!\text{ }\] Let oxidation state of Fe in                 \[{{K}_{3}}[Fe{{(OH)}_{6}}]=x\]                 \[(+\,1\,\times \,3)+x+(-1\times 6)=0\]                 \[\therefore \]  \[x=+\,3\]                 (b)  \[{{K}_{2}}[Fe{{O}_{4}}]\] Let oxidation state of Fe in \[{{K}_{2}}[Fe{{O}_{4}}]=x\]                                 \[(+1\times 2)+x+(4x-2)=0\]                                 \[x=+\,6\]                 (c) \[FeS{{O}_{4}}.{{(N{{H}_{4}})}_{2}}S{{O}_{4}}.6{{H}_{2}}O\] Let oxidation state of Fe in                 \[FeS{{O}_{4}}.{{(N{{H}_{4}})}_{2}}S{{O}_{4}}.6{{H}_{2}}O=x\]                 \[\therefore \]  \[x+(-2)+2+(-2)=0\]                                 \[x=+\,2\]                 (d) \[{{[Fe{{(CN)}_{6}}]}^{3-}}\] Let oxidation state of Fe in                                 \[{{[Fe{{(CN)}_{6}}]}^{3-}}=x\]                 \[\therefore \]  \[x+(6x-1)=-3\]                 \[\therefore \]  \[x=+\,3\] \[\therefore \]\[FeS{{O}_{4}}.{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\]has Fe in lowest  oxidation state.


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