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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2006

  • question_answer
        When\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]is converted into\[{{K}_{2}}Cr{{O}_{4}},\]the change in oxidation number of chromium is

    A)  0            

    B)  5

    C)  7                                            

    D)  9

    Correct Answer: A

    Solution :

                    Key Idea: The sum of oxidation state of all elements in a compound is always zero. Let oxidation state of Cr in \[{{K}_{2}}C{{r}_{2}}{{O}_{7}}=x\]                 \[(+1\times 2)+2x+(-2\times 7)=0\] or                \[+2+2x-14=0\] \[\therefore \]                  \[x=+6\] Let oxidation sate of Cr in \[{{K}_{2}}Cr{{O}_{4}}=x\]                 \[+1\times 2+x+(-2\times 7)=0\] \[2+x-8=0\] \[x=6\] \[\therefore \]Change in oxidation state of Cr is zero when it changes from\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]to\[{{K}_{2}}Cr{{O}_{4}}\]


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