Which of the following ions decolorizes acidic $KMnO_4$ solution?

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$FeCl_3 + Na_3PO_4 \longrightarrow FePO_4 \downarrow + 3NaCl$

$20 \ mL$ of $Fe^{2+}$ solution of certain concentration has completely reacted with $20 \ mL$ of $0.01 \ M \ K_2Cr_2O_7$ in acidic medium. If $20 \ mL$ of same $Fe^{2+}$ solution has reacted completely with $20 \ mL$ of $KMnO_4$ solution in acidic medium,the molarity of $KMnO_4$ solution is: (in $M$)

Assign $A$,$B$,$C$,$D$ from the given type of reaction.
$FeSO_4 + Na_2S \longrightarrow FeS \downarrow$

Blue colouration is not produced when :

$500$ 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 . . . . . . .