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Identify the INCORRECT statement(s) among the following:

1. In K2MnO4 and CrO2Cl2, the central transition metal ions have the same oxidation state
2. Both sodium dichromate and potassium dichromate can be used as primary standards in volumetric estimations
3. Potassium dichromate on strong heating evolves oxygen gas and forms a green powder
4. Potassium permanganate on heating with solid KOH evolves oxygen gas and forms a black powder

Correct answer: Both sodium dichromate and potassium dichromate can be used as primary standards in volumetric estimations

Solution

In K2MnO4, Mn is +6; in CrO2Cl2 (chromyl chloride), Cr is also +6 - so statement A is correct. K2Cr2O7 on strong heating gives 4K2Cr2O7 -> 4K2CrO4 + 2Cr2O3 + 3O2 (green Cr2O3 formed, O2 evolved) - statement C is correct. KMnO4 + KOH(s) on heating gives K2MnO4 + MnO2 + H2O (black MnO2 or green manganate, not O2) - statement D is incorrect. Na2Cr2O7 is hygroscopic and NOT a primary standard - statement B is incorrect.

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