Manganese belongs to group number 7 and its oxidation state in MnO₄ ⁻/KMnO₄ is also +7 i.e., KMnO4 1 + x + 4 (-2) = 0 ⇒ 1 + x – 8 = 0 ⇒ x = 7 Hence, the formula of the oxo-anion is KMnO4.
(i) Abnormal molar mass : When the molecular mass of a substance as determined by studying any of the colligative properties is different than the theoretically expected value, then the substance will have abnormal molecular mass.
(ii) Van’t Hoff factor: van't Hoff's factor (i) is defined as the ratio of the observed colligative property to the calculated colligative property. i = Observed colligative property / Calculated colligative property Observed colligative property ∝ 1/Molar Mass i = Mc/Mo Van't Hoff's factor (i) represents the extent of association (or) dissociation of a solute.