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The d-And-f-Block Elements
Question
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In acidic medium,H2O2 changes Cr2O72- to CrO5 which has two (-O-O-) bonds. Oxidation state of Cr in CrO3 is 

  • +5

  • +3

  • +6

  • -10

Answer

C.

+6

When H2O2 is added to an acidified solution of a dichromate, Cr2O72-, aO deep blue coloured complex, chromic peroxide, CrO5 [ or CrO(O2)2] is formed.
Cr2O72- +2H++4H2O2 ---> 2CrO(O2)2 +5H2O
This deep blue coloured complex.
Oxidation state of Cr is +6 due to the presence of two peroxide linkages which can be calculated as
Cr peroxide normal
x+(-1)4+(-2) =0
x-6 =0
x=+6

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Some More Questions From The d-And-f-Block Elements Chapter

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

The outer electronic configuration of copper is 3d10 4s1, yet it is considered transition element. Why?

Why the melting points of transition elements are high?

Why Zn, Cd and Hg are not regarded as transition elements?

Name the first element of 3rd transition series.

Though copper, silver and gold have completely filled sets of d-orbitals yet they are considered as transition metals. Why?

Why are transition elements so named?

Why are transition elements known as d-block elements?

Write the general electronic configuration of d-block elements.

Why do some exceptions to the general electronic configuration of d-block elements exists?