Bromine water reacts with $SO_2$ to form

One litre of $0.15 \ M$ $Na_2SO_3$ aqueous solution is mixed with $500 \ mL$ of $0.2 \ M$ $K_2Cr_2O_7$ aqueous solution in acid medium. What is the number of moles of $K_2Cr_2O_7$ remaining in the solution after the reaction?

Which of the following decolourises the colour of acidic $KMnO_4$?

In the reaction of sulphur with concentrated sulphuric acid,the oxidised product is $X$ and the reduced product is $Y$. $X$ and $Y$ are respectively:

$Fe^{3+}$ is reduced to $Fe^{2+}$ by using:
$A$. $H_2O_2$ in presence of $NaOH$
$B$. $Na_2O_2$ in water
$C$. $H_2O_2$ in presence of $H_2SO_4$
$D$. $Na_2O_2$ in presence of $H_2SO_4$

$1 \text{ mole of } H_2C_2O_4 \text{ is oxidised by } x \text{ mole of } MnO_4^- \text{ in strong basic medium and } 1 \text{ mole of } NaHC_2O_4 \text{ is oxidised by } y \text{ mole of } MnO_4^- \text{ in acidic medium. Ratio of } x/y \text{ is}$