Potassium permanganate is prepared from the mineralpyrolusite, `MnO_(2)`. Its crystals have deep purple colour. It acts as an oxidizing agent in the neutral, alkaline as well as acidic medium. In acidic medium , it is used in volumetric analysis for estimation of ferrous salts, oxalates etc. The titrations are carried out in presence of `H_(2)SO_(4)`. However ,before using it as a titrant, it is first standized with standard oxalic acid solution or Mohr salt solution. In one of the experiments on titration , 13.4 g of dry pure sodium oxalate ( molar mass `=134 g mol^(-1)` ) was dissolved in 100mLof distilled waterand then 100 mL of 2M `H_(2)SO_(4)` were added. The solution, was cooledto `25.30^(@) C`. Now to this solution , 0.1 M `KMnO_(4)` solution was added till a very faint pink colour persisted. Mohr salt, `FeSO_(4). (NH_(4))_(2) SO_(4). 6 H_(2)O` is preferred over `FeSO_(4). 7 H_(2)O` for standardization of `KMnO_(4)` solution because.A. Mohr salt is a double salt while ferrous sulphate is a single salt.B. Mohr salt is not hygroscopic but `FeSO_(4).7 H_(2)O` is hygroscopicC. Mohr slat contains only ferrous ions whereas ferrous sulphate contains some ferric ions.D. Mohr salt solution can be titrated even in the absence of `H_(2)SO_(4)`