What change does not occur when $K_2Cr_2O_7$ reacts with $H_2O_2$ solution in an acidic medium?

In acidic medium, one mole each of $MnO_4^-$ and $Cr_2O_7^{2-}$ is reduced by $x$ and $y$ moles of ferrous ions $(Fe^{2+})$ respectively. The sum of $x$ and $y$ is:

In basic medium,$CrO_{4}^{2-}$ oxidises $S_{2}O_{3}^{2-}$ to form $SO_{4}^{2-}$ and itself changes into $Cr(OH)_{4}^{-}$. The volume of $0.154 \ M \ CrO_{4}^{2-}$ required to react with $40 \ mL$ of $0.25 \ M \ S_{2}O_{3}^{2-}$ is ........... $mL$ (Rounded-off to the nearest integer).

$KMnO_4$ oxidises $I^{-}$ in acidic and neutral/faintly alkaline solution,respectively to

Identify whether the following reactions act as oxidation or reduction processes:
$(i) \ S + 6HNO_3 \to H_2SO_4 + 6NO_2 + 2H_2O$
$(ii) \ 2K + Br_2 \to 2KBr$

How many moles of $H_2SO_3$ are required to reduce one mole of $KMnO_4$ in an acidic medium?