Q.During oxidation of ferrous sulphate using mixture of dil. $H_2SO_4$ and potassium dichromate; oxidation state of chromium changes from _______.

Potassium permanganate (KMnO4) is prepared either by fusing manganese dioxide with KOH and the oxidiser KClO3 to give green potassium manganate (K2MnO4), which then disproportionates in neutral/acidic medium into purple-black KMnO4 and brown MnO2, or by electrolytically oxidising an alkaline manganate solution between iron electrodes. As an oxidiser, KMnO4 in ACIDIC medium is reduced all the way to the pale Mn2+ ion (oxidising iodide to iodine, Fe2+ to Fe3+, H2S to sulfur, and oxalic acid to CO2), while in NEUTRAL/weakly-alkaline medium it is only reduced as far as brown MnO2. Its practical uses include acting as an antiseptic, the laboratory unsaturation test, volumetric analysis of reducing agents, detecting halides, and general use as a strong laboratory/industrial oxidant. Potassium dichromate (K2Cr2O7) is manufactured industrially by roasting chromite ore (FeO.Cr2O3) with sodium carbonate and lime flux to give sodium …