CBSE 2022 · Region 5 · Set 2 · Q8 · 3 marks
Give reasons for the following statements :(a)Scandium $\displaystyle (\mathrm{Z}=21)$ is a transition element but $\displaystyle \mathrm{Zn}(\mathrm{Z}=30)$ is not.(b)$\displaystyle \left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}$ is coloured while $\displaystyle \left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ is colourless.(c)Physical and chemical properties of the 4d and 5d series of the transition elements are quite similar than expected.
Give reasons for the following statements :
(a)
Scandium $\displaystyle (\mathrm{Z}=21)$ is a transition element but $\displaystyle \mathrm{Zn}(\mathrm{Z}=30)$ is not.
(b)
$\displaystyle \left[\mathrm{Ti}\left(\mathrm{H}_{2} \mathrm{O}\right)\right]^{3+}$ is coloured while $\displaystyle \left[\mathrm{Sc}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{3+}$ is colourless.
(c)
Physical and chemical properties of the 4d and 5d series of the transition elements are quite similar than expected.
Marking-scheme solution
(a) Sc has incompletely filled 3d-orbital in its ground state but Zn atom has completely filled \(\displaystyle d\)-orbitals in its ground state as well as in its oxidised state.
(b) Due to \(\displaystyle d-d\) transition of electron in \(\displaystyle \mathrm{Ti}^{3+}\) but no d-d transition in \(\displaystyle \mathrm{Sc}^{3+}\) / Due to presence of unpaired electron in \(\displaystyle \mathrm{Ti}^{3+}\) while \(\displaystyle \mathrm{Sc}^{3+}\) does not have unpaired electrons.
(c) Due to lanthanoid contraction / due to poor shielding effect of 4f orbitals.
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)Understandshort_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.