The sodium salt of an organic acid $'X'$ produces effervescence with conc. $H_2SO_4$. $'X'$ reacts with an acidified aqueous $CaCl_2$ solution to give a white precipitate which decolourises an acidic solution of $KMnO_4$. $'X'$ is:

$SO_2$ can reduce:

$500$ 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 . . . . . . .

How much volume of $5 \ M$ $HNO_3$ is required to oxidize $16 \ g$ of $Fe^{+2}$ if $HNO_3$ is converted into $NO$? (Answer in $mL$)

In which of the following reactions is there no change in the valency (oxidation state) of the elements?

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