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Chemistry · 2024 · 5 marks
The d-and f-Block ElementsElectronic Configurations of the d-Block Elements5 marksUnderstandlong answer
CBSE 2024 · Region 4 · Set 1 · Q31
Attempt any five of the following: (a) Why Zinc is not regarded as a transition element? (b) What is Lanthanoid contraction? (c) Why is first…
Attempt any five of the following :
(a)
Why Zinc is not regarded as a transition element ?
(b)
What is Lanthanoid contraction ?
(c)
Why is first ionization enthalpy of chromium lower than that of Zn ?
(d)
Why are transition elements good catalysts ?
(e)
Compounds of transition metals are generally coloured. Give reason.
(f)
Out of $\displaystyle \mathrm{KMnO}_{4}$ and $\displaystyle \mathrm{K}_{2} \mathrm{MnO}_{4}$, which one is paramagnetic and why ?
(g)
Complete the following ionic equation : \[\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}+14 \mathrm{H}^{+}+6 \mathrm{e}^{-} \longrightarrow \] $\displaystyle \mathbf{1} \boldsymbol{\times} \mathbf{5}$
Marking-scheme solution
(a) Zn hasfully filled d-orbital configuration in ground state and in its oxidized state.
(b) The filling of 4f orbital before 5d orbital results in steady decrease in atomic radii and ionic radii. / The steady decrease in the atomic radii or ionic radii of the elements with increase in atomic number.
(c) In chromium an electron is removed from \(\displaystyle 4 s^{1}\) while in Zn it is from fully filled \(\displaystyle 4 s^{2}\) orbital.
(d) Due to variable oxidation stateandcomplex formation /provide large surface area.
(e) Due to d-d transition of electrons in d- orbitals / unpaired electrons in d-orbital.
(f) \(\displaystyle \mathrm{K}_{2} \mathrm{MnO}_{4}\), due to the presence of one unpaired electron.
(g) \(\displaystyle \mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}+14 \mathrm{H}^{+}+6 \mathrm{e}^{-} \longrightarrow 2 \mathrm{Cr}^{3+}+7 \mathrm{H}_{2} \mathrm{O}\)
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CBSE Class 12 Chemistry past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.