If salt $Q$ undergoes a redox reaction with $H_2S$ in an acidic medium,then which of the following species cannot be a possible product?

Bromine water reacts with $SO_2$ to form

$Zn_{(s)} + CuSO_{4(aq)} \rightarrow ZnSO_{4(aq)} + Cu_{(s)}$ is an example of which type of process?

Calculate the millimoles of $SeO_3^{2-}$ in solution on the basis of following data: $70 \ mL$ of $\frac{M}{60}$ solution of $KBrO_3$ was added to $SeO_3^{2-}$ solution. The bromine evolved was removed by boiling and excess of $KBrO_3$ was back titrated with $12.5 \ mL$ of $\frac{M}{25}$ solution of $NaAsO_2$. The reactions are given below.
$I. \ SeO_3^{2-} + BrO_3^{-} + H^{+} \to SeO_4^{2-} + Br_2 + H_2O$
$II. \ BrO_3^{-} + AsO_2^{-} + H_2O \to Br^{-} + AsO_4^{3-} + H^{+}$

$X(aq.) + Na_2O_2 \to Y(aq.) \xrightarrow{BaCl_2} Z \downarrow_{\text{Insoluble in dil. } HCl}$
$X$ and $Y$ are different sodium salts. Then the anion present in the salt $(X)$ is:

Acidified potassium permanganate solution is decolourised by