Acidified potassium permanganate solution is decolourised by

Which of the following species is both basic and a reducing agent?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$Pb(CH_3COO)_2 + Na_2CrO_4 \longrightarrow PbCrO_4 \downarrow + 2CH_3COONa$

Acidified $K_2Cr_2O_7$ solution turns green when $Na_2SO_3$ is added to it. This is due to the formation of

Chlorine oxidises sulphur dioxide in the presence of water to give an oxyacid $A$. Chlorine also oxidises iodine in the presence of water to give an oxyacid $B$. The oxidation states of $S$ and $I$ in $A$ and $B$ are respectively

$X + H_2SO_4 \to Y$ (colorless gas) and $Y + K_2Cr_2O_7 + H_2SO_4 \to$ green solution. Then $X$ and $Y$ are respectively ........