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Chemistry · 2023 · 5 marks
CBSE 2023 · Region 5 · Set 1 · Q35
(a) Why is chemistry of actinoids complicated as compared to lanthanoids? (b) Complete the following reaction and justify that it is a…
(a)
Why is chemistry of actinoids complicated as compared to lanthanoids ? \[\]
(b)
Complete the following reaction and justify that it is a disproportionation reaction : $\displaystyle 3 \mathrm{MnO}_{4}{ }^{2-}+4 \mathrm{H}^{+} \rightarrow$ + $\displaystyle +2 \mathrm{H}_{2} \mathrm{O}$.
(c)
The given graph shows the trends in melting points of transition metals :
Explain the reason why Cr has highest melting point and manganese (Mn) a lower melting point.
Marking-scheme solution
(a)
Actinoids show wide range of oxidation states / most of them are radioactive elements.
\[\text { (b) } 3 \mathrm{MnO}_{4}^{2-}+4 \mathrm{H}^{+} \longrightarrow+2 \mathrm{MnO}_{4}^{-}+\mathrm{MnO}_{2}+2 \mathrm{H}_{2} \mathrm{O}
\]
Oxidation state of Mn increases from +$\displaystyle 6$ to + $\displaystyle 7$ (oxidation) and decreases from + $\displaystyle 6$ to + $\displaystyle 4$ (reduction) / Mn undergoes increase and decrease in oxidation state simultaneously.
(c)
Due to the presence of a greater number of unpaired electrons which leads to strong interatomic metal-metal bonding whereas Mn with a stable half-filled \(\displaystyle \mathrm{d}^{5}\) configuration has a weaker metallic bond.
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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.