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Chemistry · 2023 · 5 marks
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)5 marksUnderstandlong answer
CBSE 2023 · Region 2 · Set 1 · Q33
(a) (I) Account for the following: 3 + 2 (i) E^o value for Mn^3+ / Mn^2+ couple is much more positive than that for Cr^3+ / Cr^2+. (ii) Sc^3+ is…
(I)
Account for the following: $\displaystyle 3$ + $\displaystyle 2$
(i)
$\displaystyle \mathrm{E}^{\mathrm{o}}$ value for $\displaystyle \mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}$ couple is much more positive than that for $\displaystyle \mathrm{Cr}^{3+} / \mathrm{Cr}^{2+}$.
(ii)
$\displaystyle \mathrm{Sc}^{3+}$ is colourless whereas $\displaystyle \mathrm{Ti}^{3+}$ is coloured in an aqueous solution.
(iii)
Actinoids show wide range of oxidation states.
(II)
Write the chemical equations for the preparation of $\displaystyle \mathrm{KMnO}_{4}$ from $\displaystyle \mathrm{MnO}_{2}$.
(I)
Account for the following:
(i)
Transition metals form alloys.
(ii)
$\displaystyle \mathrm{Ce}^{4+}$ is a strong oxidising agent.
(II)
Write one similarity and one difference between chemistry of Lanthanoids and Actinoids.
(III)
Complete the following ionic equation: $\displaystyle \mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+2 \mathrm{OH}^{-} \longrightarrow$
Marking-scheme solution
(a) (I)
(i) \(\displaystyle \mathrm{Cr}^{2+}\) changes from \(\displaystyle \mathrm{d}^{4}\) to stable half-filled \(\displaystyle \mathrm{t}_{2 \mathrm{~g}}{ }^{3}\) configuration while \(\displaystyle \mathrm{Mn}^{3+}\) changes to stable half-filled d \(\displaystyle { }^{5}\) configuration.
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CBSE Class 12 Chemistry past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.