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D and F Block Elements question

2022 · 27 Jul · Shift 1 · Q7
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  5. /2022 · 27 Jul · Shift 1 · Q7

D and F Block Elements question

2022 · 27 Jul · Shift 1 · Q7

JEE MainChemistryD and F Block ElementsMCQ+4 / −1
Given below are two statements. Statement I : Iron (III) catalyst, acidified K2Cr2O7\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}K2​Cr2​O7​ and neutral KMnO4\mathrm{KMnO}_{4}KMnO4​ have the ability to oxidise I−\mathrm{I}^{-}I− to I2\mathrm{I}_{2}I2​ independently. Statement II : Manganate ion is paramagnetic in nature and involves pπ−pπ\mathrm{p} \pi-\mathrm{p} \pipπ−pπ bonding. In the light of the above statements, choose the correct answer from the options given below.
  1. A
    Both Statement I and Statement II are true.
  2. B
    Both Statement I and Statement II are false.
  3. C
    Statement I is true but Statement II is false.
  4. D
    Statement I is false but Statement II is true.
View written solutionFree

Correct answer: C

  1. Check Statement I

    Statement I says: Iron (III) catalyst, acidified K2Cr2O7\mathrm{K_2Cr_2O_7}K2​Cr2​O7​ and neutral KMnO4\mathrm{KMnO_4}KMnO4​ can independently oxidise I−\mathrm{I^-}I− to I2\mathrm{I_2}I2​.

    We examine each oxidising agent:

    • Acidified K2Cr2O7\mathrm{K_2Cr_2O_7}K2​Cr2​O7​ is a strong oxidising agent and does oxidise iodide to iodine: Cr2O72−+14H++6I−→2Cr3++3I2+7H2O\mathrm{Cr_2O_7^{2-} + 14H^+ + 6I^- \rightarrow 2Cr^{3+} + 3I_2 + 7H_2O}Cr2​O72−​+14H++6I−→2Cr3++3I2​+7H2​O So this part is true.

    • Neutral KMnO4\mathrm{KMnO_4}KMnO4​ also oxidises iodide to iodine: 2MnO4−+6I−+4H2O→2MnO2+3I2+8OH−\mathrm{2MnO_4^- + 6I^- + 4H_2O \rightarrow 2MnO_2 + 3I_2 + 8OH^-}2MnO4−​+6I−+4H2​O→2MnO2​+3I2​+8OH− So this part is true.

    • Iron(III): Fe3+\mathrm{Fe^{3+}}Fe3+ can oxidise iodide to iodine because 2Fe3++2I−→2Fe2++I2\mathrm{2Fe^{3+} + 2I^- \rightarrow 2Fe^{2+} + I_2}2Fe3++2I−→2Fe2++I2​ This is feasible since E∘(Fe3+/Fe2+)=+0.77 V,E∘(I2/I−)=+0.54 VE^\circ(\mathrm{Fe^{3+}/Fe^{2+}})=+0.77\,\text{V}, \qquad E^\circ(\mathrm{I_2/I^-})=+0.54\,\text{V}E∘(Fe3+/Fe2+)=+0.77V,E∘(I2​/I−)=+0.54V Hence, Ecell∘=0.77−0.54=+0.23 V>0E^\circ_{\text{cell}} = 0.77 - 0.54 = +0.23\,\text{V} > 0Ecell∘​=0.77−0.54=+0.23V>0 Therefore Fe3+\mathrm{Fe^{3+}}Fe3+ can oxidise I−\mathrm{I^-}I− to I2\mathrm{I_2}I2​.

    Thus, Statement I is true.

  2. Check Statement II

    Statement II says: Manganate ion is paramagnetic in nature and involves pπ−dπ\mathrm{p\pi-d\pi}pπ−dπ bonding?

    But the given statement says it involves pπ−pπ\mathrm{p\pi-p\pi}pπ−pπ bonding.

    For manganate ion, MnO42−\mathrm{MnO_4^{2-}}MnO42−​:

    • Oxidation state of Mn is +6+6+6.
    • Mn electronic configuration in ground state: [Ar]3d54s2[Ar]3d^54s^2[Ar]3d54s2
    • Therefore Mn6+:[Ar]3d1\mathrm{Mn^{6+}}: [Ar]3d^1Mn6+:[Ar]3d1

    So manganate has one unpaired electron, hence it is paramagnetic.

    However, the multiple bonding in oxyanions of transition metals like MnO42−\mathrm{MnO_4^{2-}}MnO42−​ is described as pπ−dπp\pi-d\pipπ−dπ bonding, not pπ−pπp\pi-p\pipπ−pπ bonding.

    Therefore, Statement II is false.

  3. Conclusion

    • Statement I: True
    • Statement II: False

    Hence the correct option is: C\boxed{\text{C}}C​

  4. Comparison with stored answer

    Stored correct answer is B, but our derived answer is C.

    So the stored answer appears to be incorrect.

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