Acidified potassium permanganate solution is decolourised by

$500$ 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 . . . . . . .

The oxidation state of manganese in the product obtained in a reaction of potassium permanganate and hydrogen peroxide in basic medium is $.....$

$SO_2$ can reduce:

Light green crystals of ferrous sulphate lose water molecules and turn brown on exposure to air. This is due to its oxidation to:

Reduction of the metal centre in aqueous permanganate ion involves