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The d-And-f-Block Elements

Short Answer Type

241.

Assign reasons for the following:
Transition metals and their many compounds act as good catalyst.

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242.

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

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243. The E° value for the Mn³⁺/Mn²⁺ couple is much more positive than that for Cr³⁺/Cr²⁺ or Fe³⁺/Fe²⁺? Explain.

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244.

Scandium (Z = 21) does not exhibit variable oxidation states and yet it is regarded as a transition element.

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245.
What may be the possible oxidation states of the transition metals with the following d electronic configurations in the ground state of their atoms: 3d³4s²,3d⁵4s² and 3d⁶4s². Indicative relative stability of oxidation states in each case.

(a) Configuration

3d³4s²

3d⁵ 4s²

3d⁶ 4s²

(a) Stable oxidation state

+3, +3

+2, +7

+2, +8

The stability of any oxidation state of any element generally depends upon the electronic configuration of that particular ion. If any ion has stable configuration (d⁵, d¹⁰ etc.), the particular oxidation state will be more stable.

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Long Answer Type

246. Write steps involved in the preparation of (i) Na₂CrO₄ from chromite ore and (ii) K₂MnO₄ from pyrolusite ore.

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Fill In the Blanks

247. The spin magnetic moment is given by the formula _____________.

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248.

The outermost electronic configuration of Cr is ___________.

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249.

The property of paramagnetism is due to the presence of _________ electrons.

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250. The d-block elements are also called _________.

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