Which of the following reactions does not involve either oxidation or reduction?

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

$10 \, \text{mole}$ of ferric oxalate is oxidised by $x \, \text{mole}$ of $MnO_4^-$ in acidic medium. The value of $x$ is

$500$ mL of $0.2$ $M$ $MnO_4^-$ solution in basic medium when mixed with $500$ mL of $1.5$ $M$ $KI$ solution,oxidises iodide ions to liberate molecular iodine. This liberated iodine is then titrated with a standard $x$ $M$ thiosulphate solution in presence of starch. If $300$ mL of thiosulphate was consumed,then the value of $x$ is . . . . . . .

When mercury $(II)$ chloride is treated with excess of $SnCl_2$,the products obtained are

$A$ few drops of $KMnO_4$ solution are added to an acidic solution containing an anion. Which of the following,if present,will $NOT$ cause a change in the color of the $KMnO_4$ solution?