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RAJASTHAN ­ PET Rajasthan PET Solved Paper-2008

  • question_answer
    The oxidation number of Cr is changed on reaction of acidic\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]with\[{{H}_{2}}S\]

    A)  + 3 to + 6        

    B)  + 6 to + 3

    C)  + 6 to + 2        

    D)  remains unchanged

    Correct Answer: B

    Solution :

     The reaction of acidic\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]with\[{{H}_{2}}S\]is as \[\underset{O.N.=+6}{\mathop{C{{r}_{2}}O_{7}^{2-}}}\,+14{{H}^{+}}+3{{S}^{2-}}\xrightarrow[{}]{{}}\underset{O.N.=+3}{\mathop{2C{{r}^{3+}}}}\,\]     \[+3S+7{{H}_{2}}O\] Hence, the oxidation number of Cr changes + 6 to +3.


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