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D and F Block Elements question

2020 · 4 Sep · Shift 2 · Q4
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D and F Block Elements question

2020 · 4 Sep · Shift 2 · Q4

JEE MainChemistryD and F Block ElementsMCQ+4 / −1
The incorrect statement(s) among (a) - (c) is (are) (a) W(VI) is more stable than Cr(VI). (b) In the presence of HCl, permanganate titrations provide satisfactory results. (c) Some lanthanoid oxides can be used as phosphors.
  1. A
    (a) and (b) only
  2. B
    (a) only
  3. C
    (b) only
  4. D
    (b) and (c) only
View written solutionFree

Correct answer: C

  1. We must identify the incorrect statement(s) among (a)–(c).
  1. Check statement (a): W(VI)\mathrm{W(VI)}W(VI) is more stable than Cr(VI)\mathrm{Cr(VI)}Cr(VI).
  • In group 6, higher oxidation states become more stable as we move down the group due to better participation of heavier d-orbitals.
  • Thus, for tungsten, the oxidation state +6+6+6 is highly stable.
  • Chromium(VI) is also known, but it is a stronger oxidizing state and less stable relative to tungsten(VI).

Hence, (a) is correct.

  1. Check statement (b): In the presence of HCl, permanganate titrations provide satisfactory results.
  • KMnO4\mathrm{KMnO_4}KMnO4​ is a strong oxidizing agent.
  • In acidic medium for permanganate titrations, dilute H2SO4\mathrm{H_2SO_4}H2​SO4​ is used.
  • HCl\mathrm{HCl}HCl is not used because chloride ions are oxidized by permanganate to chlorine:
2MnO4−+16H++10Cl−→2Mn2++8H2O+5Cl22\mathrm{MnO_4^-} + 16\mathrm{H^+} + 10\mathrm{Cl^-} \rightarrow 2\mathrm{Mn^{2+}} + 8\mathrm{H_2O} + 5\mathrm{Cl_2}2MnO4−​+16H++10Cl−→2Mn2++8H2​O+5Cl2​
  • This causes side reaction and interferes with the titration.

Hence, (b) is incorrect.

  1. Check statement (c): Some lanthanoid oxides can be used as phosphors.
  • Yes, lanthanoid compounds/oxides are widely used in phosphors because of their characteristic electronic transitions.
  • For example, europium- and terbium-containing materials are used in luminescent applications.

Hence, (c) is correct.

  1. Therefore, only statement (b) is incorrect.

So the correct option is:

C: (b) only\boxed{\text{C: (b) only}}C: (b) only​
  1. Comparison with stored correct answer:
  • Stored correct answer: C
  • Derived answer: C

They agree.

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