CBSE 2025 · Region 4 · Set 2 · Q26 · 3 marks
Give explanation for each of the following observations :(a)With the same d-orbital configuration $\displaystyle \left(\mathrm{d}^{4}\right), \mathrm{Mn}^{3+}$ ion is an oxidising agent whereas $\displaystyle \mathrm{Cr}^{2+}$ ion is a reducing agent.(b)Actinoid contraction is greater from element to element than that among lanthanoids.(c)Transition metals form large number of interstitial compounds with H, B, C and N.
Give explanation for each of the following observations :
(a)
With the same d-orbital configuration $\displaystyle \left(\mathrm{d}^{4}\right), \mathrm{Mn}^{3+}$ ion is an oxidising agent whereas $\displaystyle \mathrm{Cr}^{2+}$ ion is a reducing agent.
(b)
Actinoid contraction is greater from element to element than that among lanthanoids.
(c)
Transition metals form large number of interstitial compounds with H, B, C and N.
Marking-scheme solution
(a)
Change from Mn3+ to Mn2+ results in extra stable half filled d5 configuration.
Cr2+ is reducing as its configuration changes from d4 to d3 which is stable half filled t2g3
configuration.
(b)
Due to poorer shielding offered by 5f electrons than 4f.
(c)
H, B, C and N atoms being small in size get trapped inside the crystal lattices of transition
metals.
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)Understandshort_answerhard
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CBSE Class 12 Chemistry past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.