Which of the following is a redox reaction?

For the reaction $Cr_2O_7^{2-} \xrightarrow{H^+} Cr^{3+}$,what is the equivalent weight of $Cr_2O_7^{2-}$?

$KMnO_4$ acts as an oxidising agent in acidic medium. The number of moles of $KMnO_4$ that will be needed to react with one mole of sulphide ion $(S^{2-})$ in acidic solution is . . . . . . (in $/5$)?

Observe the following reaction:
$xS_{8\text{(s)}} + yOH^{-}{_{\text{(aq)}}} \rightarrow zS^{2-}{_{\text{(aq)}}} + 2S_2O_3^{2-}{_{\text{(aq)}}} + 6H_2O_{\text{(l)}}$
Find the values of $x, y$ and $z$ respectively.

In alkaline medium,the reduction of permanganate anion involves a gain of $........$ electrons.

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Na_2CrO_4 + HCl \longrightarrow H_2Cr_2O_7 + NaCl$