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Chemistry · 2022 · 3 marks
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)3 marksUnderstandshort answer
CBSE 2022 · Region 1 · Set 2 · Q11
(a) Account for the following: (i) Transition metals and their compounds act as good catalysts. (ii) Eu^2+ is a strong reducing agent. (iii) Chromium…
(a)
Account for the following :
(i)
Transition metals and their compounds act as good catalysts.
(ii)
$\displaystyle \mathrm{Eu}^{2+}$ is a strong reducing agent.
(iii)
Chromium is hard whereas Zinc is soft metal.
OR
(b)
What is Lanthanoid contraction ? Write two consequences of Lanthanoid contraction.
Marking-scheme solution
(a) (i) Variable or multiple oxidation state / ability to form complexes / they provide large surface area for adsorption (utilises (n-$\displaystyle 1$)d and ns electrons for bonding).
(ii) Because Eu is more stable in common +$\displaystyle 3$ oxidation state.
(iii) Because of strong metallic bonding in Cr and weak metallic bonding in Zn / presence of unpaired electrons in Cr whereas no unpaired electron in Zn.
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CBSE Class 12 Chemistry past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.