Which of the following reactions are redox reactions?
$I. \, Cr_2O_7^{2-} + 2OH^- \to 2CrO_4^{2-} + H_2O$
$II. \, Zn + CuSO_4 \to ZnSO_4 + Cu$
$III. \, 2MnO_4^- + 3Mn^{2+} + 4OH^- \to 5MnO_2 + 2H_2O$
$IV. \, 2Cu^+ \to Cu + Cu^{2+}$

  • A
    $I, II$
  • B
    $I, III$
  • C
    $III, IV$
  • D
    $II, III, IV$

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Which one of the following reactions does not take place?

Which of the following oxidation reactions are carried out by both $K_2Cr_2O_7$ and $KMnO_4$ in acidic medium?
$A. I^{-} \rightarrow I_2$
$B. S^{2-} \rightarrow S$
$C. Fe^{2+} \rightarrow Fe^{3+}$
$D. I^{-} \rightarrow IO_3^-$
$E. S_2O_3^{2-} \rightarrow SO_4^{2-}$
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$H_2S$ ($5$ moles) reacts completely with acidified aqueous potassium permanganate solution. In this reaction,the number of moles of water produced is $x$,and the number of moles of electrons involved is $y$. The value of $(x+y)$ is. . . . . .

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