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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 3 · Set 2 · Q4
Account for the following: (i) Cr^2+ is a strong reducing agent. (ii) Ti^3+ is coloured whereas Sc^3+ is colourless in aqueous solution. (iii) Zn, Cd…
Account for the following :
(i)
$\displaystyle \mathrm{Cr}^{2+}$ is a strong reducing agent.
(ii)
$\displaystyle \mathrm{Ti}^{3+}$ is coloured whereas $\displaystyle \mathrm{Sc}^{3+}$ is colourless in aqueous solution.
(iii)
Zn, Cd and Hg are not called transition elements.
Marking-scheme solution
(i) Because Cr is more stable in +$\displaystyle 3$ oxidation state due to stable \(\displaystyle t_{2 g}^{3}\) configuration
(ii) Because of the presence of unpaired electron in 3d-orbital of \(\displaystyle \mathrm{Ti}^{3+}\) whereas \(\displaystyle \mathrm{Sc}^{3+}\) has no unpaired electron / \(\displaystyle \mathrm{Ti}^{3+}\) shows d-d transition while \(\displaystyle \mathrm{Sc}^{3+}\) does not.
(iii) Because of completely filled \(\displaystyle d\)-orbital in the ground state or in any of its oxidation state.
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