The products of the chemical reaction between $Na_2S_2O_3$,$Cl_2$ and $H_2O$ are

$100 \, mL$ of a sample containing calcium oxalate $[CaC_2O_4]$ is dissolved in an acidic solution. It required $20 \, mL$ of $1 \, M \, KMnO_4$ for complete oxidation. Find the mass of $Ca^{2+}$ ions (in grams) present in the sample. [Atomic mass of $Ca = 40$]

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

Which of the following reactants can be reduced by $SO_2$ in the given reactions?
$(I)$ $O_3 \to$ product
$(II)$ $Cr_2O_7^{2-} \xrightarrow{H^{+}} $ product
$(III)$ $MnO_4^{-} \xrightarrow{H^{+}} $ product
$(IV)$ $H_2S \to$ product

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

$Na_2S_2O_3$ is