Which of the following reagents forms a green precipitate $(ppt)$ with $KI$?

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

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

The volume,in $mL$,of $0.02 \ M \ K_2Cr_2O_7$ solution required to react with $0.288 \ g$ of ferrous oxalate $(FeC_2O_4)$ in acidic medium is........
(Molar mass of $Fe = 56 \ g \ mol^{-1}$)

Which of the following is not formed when $H_2S$ reacts with acidic $K_2Cr_2O_7$ solution?

Which of the following occurs with $KMnO_4$ in neutral or faintly alkaline medium?