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Among the statements (a)-(c), which is/are INCORRECT? (a) W(VI) is more stable than Cr(VI). (b) In the presence of HCl, permanganate titrations give satisfactory results. (c) Some lanthanoid oxides can be used as phosphors.

1. (a) and (b) only
2. (a) only
3. (b) and (c) only
4. (b) only

Correct answer: (b) only

Solution

Statement (a) is correct (higher oxidation states are more stable down a group, so W(VI) > Cr(VI) stability) and (c) is correct, but (b) is wrong because HCl is oxidised by MnO4-, giving misleading results.

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