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D and F Block Elements question

2021 · 31 Aug · Shift 1 · Q2
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D and F Block Elements question

2021 · 31 Aug · Shift 1 · Q2

JEE MainChemistryD and F Block ElementsMCQ+4 / −1
In the structure of the dichromate ion, there is a :
  1. A
    linear symmetrical Cr−O−CrCr-O-CrCr−O−Cr bond.
  2. B
    non-linear symmetrical Cr−O−CrCr-O-CrCr−O−Cr bond.
  3. C
    linear unsymmetrical Cr−O−CrCr-O-CrCr−O−Cr bond.
  4. D
    non-linear unsymmetrical Cr−O−CrCr-O-CrCr−O−Cr bond.
View written solutionFree

Correct answer: B

  1. Identify the ion and its structure

    The dichromate ion is Cr2O72−Cr_2O_7^{2-}Cr2​O72−​.

    It consists of two tetrahedral CrO4CrO_4CrO4​ units sharing one oxygen atom.

    So its basic connectivity is: O3Cr−O−CrO3O_3Cr-O-CrO_3O3​Cr−O−CrO3​

  2. Nature of the bridging Cr−O−CrCr-O-CrCr−O−Cr linkage

    Since each chromium is surrounded approximately tetrahedrally by oxygen atoms, the shared oxygen connects the two tetrahedra.

    A tetrahedral arrangement does not allow the Cr−O−CrCr-O-CrCr−O−Cr linkage to be linear. Therefore, the bond angle ∠Cr−O−Cr\angle Cr-O-Cr∠Cr−O−Cr is bent (non-linear).

  3. Check symmetry of the linkage

    In dichromate, the bridging oxygen is bonded to two equivalent chromium atoms. Both chromium atoms are in the same oxidation state +6+6+6 and are in similar tetrahedral environments.

    Hence, the bridging arrangement is symmetrical with respect to the Cr−O−CrCr-O-CrCr−O−Cr bond.

  4. Evaluate the options

    • A: linear symmetrical Cr−O−CrCr-O-CrCr−O−Cr bond →\rightarrow→ Incorrect
    • B: non-linear symmetrical Cr−O−CrCr-O-CrCr−O−Cr bond →\rightarrow→ Correct
    • C: linear unsymmetrical Cr−O−CrCr-O-CrCr−O−Cr bond →\rightarrow→ Incorrect
    • D: non-linear unsymmetrical Cr−O−CrCr-O-CrCr−O−Cr bond →\rightarrow→ Incorrect

  5. Final answer

    The dichromate ion has a non-linear symmetrical Cr−O−CrCr-O-CrCr−O−Cr bond.

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