$KMnO_4$ oxidises $C_2H_2O_4$ to form $CO_2$. In which of the following,the reaction will be faster?

Which of the following reactions will lead to a redox reaction?

$KI$ is oxidised into $I_2$ by using the reagent

In neutral or faintly alkaline medium,$MnO_4^{-}$ oxidizes $I^{-}$ to iodate. What is the number of moles of $KMnO_4$ required to completely convert $1 \ L$ of $0.5 \ M \ KI$ to iodate?

Which one is the oxidising agent in the reaction below?
$2CrO_4^{2-} + 2H^{+} \to Cr_2O_7^{2-} + H_2O$

$50 \ mL$ of $0.1 \ M$ solution of a salt reacted with $25 \ mL$ of $0.1 \ M$ solution of sodium sulphite. The half-reaction for the oxidation of sulphite ion is:
$SO_{3}^{2-} (aq) + H_{2}O (l) \to SO_{4}^{2-} (aq) + 2H^{+} (aq) + 2e^{-}$
If the oxidation number of the metal in the salt was $+3$,what would be the new oxidation number of the metal?